Okay, we all love to make up our own chapters, and we want to make them the biggest, most badass ass-kickers this side of the Golden Throne. Fact is, a lot of people need a little help keeping it canon-friendly(I know I did). So that's what this is for: just a few tips to help make a canon-friendly Chapter; please feel free to add to or edit this if you see anything missing.Jochannon 08:59, October 27, 2010 (UTC)
Note: much of the text here has been copied from Lexicanum under the Fair Use doctrine.
When creating your chapter's page, please use the Space Marine Chapter Infobox to keep things in order.
Before You StartEdit
There are a lot of Chapters already on this Wiki, so look around, there may already be a chapter like the one you want to make; no-one wants to be accused of Plagiarism.
To check different chapters, here are the Space Marines categories that can be used as lists now:
Co-operative Chapters, like the Dragon Brothers are Open Groups, Space Marine Chapters that anyone can write for: check out the category for more.
Writing for a Co-op Chapter can give you valuable experience writing in the universe of WH40K, in dealing with Space Marines, and lets you write with an established chapter with connections in the fanon.
Saving the UniverseEdit
We all want to save the universe, and we all want our Chapters' names to ring across the Imperium. But there are more than enough heroic deeds to go around, inflating them beyond the practical just comes off as tacky. Driving away a Tyranid Splinter Fleet is heroic enough, destroying an entire hive fleet single-handedly just looks supercilious.
What is a Chapter?Edit
A Space Marine Chapter is a self-contained army. It is usually made of up to a thousand Space Marines, as well as a large number of administrative and functionary personnel.
Each Chapter is an independent army, with its own leadership, support and administrative staff, reliant only on its own Chapter members and its own resources. Each chapter has its own traditions, specialities, its own cult, beliefs and practices.
Codex and non-Codex ChaptersEditThe Codex Astartes is the template on which the vast majority of Chapters are based. A 'Codex Chapter' which closely (if not completely) follows the doctrines of the Codex Astartes, is led by a Chapter Master and made up of ten companies, each consisting of up to one hundred Marines and commanded by an officer with the rank of Captain. The First Company is made up of the Chapter's most experienced veterans, while the second through ninth consist of more ordinary warriors. Some individual companies may be specialized assault or support companies, possessing larger proportions of Assault or Devastator squads. The tenth company is a Scout force, made up of aspiring Space Marines not yet proven in battle.
There is no reason why you cannot make a non-Codex Chapter, but the Codex is the baseline: start with a Codex Chapter, and then implement the changes you want to make. You should work out exactly why the Chapter made those changes in the first place: it could be because your Chapter encounters some unique battle conditions, or suffered such heavy losses they needed to change a lot simply to survive.
In general, no Chapter diverges from the Codex without a strong reason to do so.
The reason to divide the Space Marine Legions to chapters after the Horus Heresy, was to prevent any man from commanding so many warriors again: 1,000 is the limit. There are exceptions, but those are extremely rare. You should not try to make a chapter with over 1,000 battle-brothers without very good reason.
Really the only reason why a Chapter would be permitted to be big is because people don't know. For example the Black Templars who are suspected to number over 6000 brothers are a fleet based crusader chapter and therefore are very difficult to keep track of.
The Fortress-monastery is an enormous fortress where the Chapter has its headquarters. Chapters are highly monastic as well as military organizations, their fighting members are all warrior-monks, their fortress-monasteries devoted both to battle and worship.
Fortress-monasteries are usually based on Imperial worlds, which the Chapter Master is sometimes also the planetary governor of. In other cases the Chapter Master will make a deal with the existing planetary governor, paying a tithe in return for the land they occupy. Deserted moons or asteroids are also possible locations of a Fortress-Monastery. In the case of fleet-based chapters the chapter's flagship serves as a mobile fortress-monastery. The locations of some chapter planets are hidden while others are well-known.
When making your Chapter, you should also write out some details about the Fortress-Monastery; it's very important in the lives of the Chapter.
Also Chapters may be given solar systems to control or look after and may have a dozen planets or so to look after, usually this is an honour given in gratitude or because that Chapter has a specific role to play in a certain part of the Galaxy. A reason for your chapter controlling any worlds beyond their home world must be provided, these worlds can also include chapter recruitment worlds which often tend to be feral worlds which the Imperium has little interest in.
Planet-based Chapters recruit primarily from their homeworld, while fleet-based Chapters may recruit haphazardly from the worlds they stop at, or may have a regular 'route' of worlds they recruit from.
Feral and Hive worlds are the most popular grounds from which chapters draw their recruits from, primarily due to a hard life style or warrior traditions of the inhabitants of those worlds. Some chapters like the Ultramarines may also base their recruits on bloodlines for example Uriel Ventris was permitted to be tested to join the Ultramarines because he was related to a decorated Sergeant of the 1st Company who died during the Tyranid assault on Macragge.
Besides the Space Marine fighting brethren, there are many non-combat personnel, fully part of the Chapter but generally not involved directly in combat. These include the chapter's hereditary slaves, Astropaths, Navigators, etc.
While we all have a tendency to focus on the actual ass-kicking Marines, no Chapter can function without these people: they tend the forges, repair the equipment, man the guns, transmit information, and protect the Chapter's home while the Marines are out kicking ass. They do not however form a regiment of their own that fights beside the Space Marines on all fronts.
The creation of a new Chapter is known as a Founding, and it does not happen overnight. Each Chapter is created from the gene-seed of an existing donor Chapter (usually one of the original nine). The zygote is implanted in a human test-slave who spends his entire life in a static experimental capsule, immobile and serving nothing but as a medium which from two progenoids will develop. When the progenoids are developed, they are extracted from the original test-slave and then implanted into another two test-slaves, producing four progenoids, and so on. It takes 55 years of reproduction to create a healthy set of 1,000 organs. These must be sanctioned officially by the Master of the Adeptus Mechanicus and then by the High Lords of Terra, speaking for the Emperor, who alone can give permission for the creation of a new Chapter.
Why was this Chapter founded? Do they have some specific purpose to fulfill? What campaigns have they fought in, what honors have they earned?
All chapters are "founded" from an already existing chapter, even if it does not have to be stated. You can create a chapter of "unknown geneseed" and it is completely OK, because the Founding chapter's tactics and general behavious decide a lot about the successor chapter. Like how the Ultramarines and their successors are Codex Chapters, and how the Blood Angels and theirs are assault specialists.
Yes, everyone can agree the Grey Knights (-cough- 4TH EDITION!!!) are badass. This fanon does permit you to expand upon the Knights, you could do a special detachment of Grey Knights within the chapter or something equally interesting. It is a big chapter, just as long as you don't bend the canon too much.
However, it is not okay to create a fanon chapter that is of Grey Knight origins, so don't do it.
Legion 1: Dark AngelsEditThe Dark Angels have a vaunted, but grim reputation among the ranks of the Astartes, and their successors tend to take after their parent Chapter more than most. In fact the Chapters descended from the Gene-seed of Lion El'Johnson even have a collective name: The Unforgiven. The Unforgiven tend to take after their predessesor in a number of ways. The Dark Angels tend to be a grim, brooding presence when compared with Chapters of other lineages. They spurn glory and flashy baubals, and cut a somewhat unfriendly figure. This is because of their secret shame, the Fallen. The Unforgiven seek to both hide, and wash away that stain upon their honor. Thus they do not seek to grow close to those outside the Unforgiven, lest their secret become known. This has made them especially wary of the Inquisition, and the two sides do not get along. Likewise since they are very conscious of their honor, and anything that may blemish it they tend to be very orthodox in their beliefs, sometimes to an extreme extent. This is why they refuse to fight alongside mutants or Abhumans. In the Imperium the Dark Angels' geneseed is seen as unpopular for the creation of new Chapters because of the secrets surrounding the Unforgiven, the fact that they don't tend to play well with others and because they have been known to abandon their duties to pursue their own unkown agendas (chasing the Fallen Angels). Unforgiven tend to be Semi-Codex Chapters. They follow the Codex is most respects, but often their 1st and 2nd Companies are modelled after the Dark Angels' Deathwing and Ravenwing. As stated the Unforgiven aren't the most friendly of Chapters, and they have a particularly bad relationship with the Inquisition. They also have a rivalry with the Space Wolves. So if
your Unforgiven Chapter happens to run into them it is a good excuse for some hostility. Remember that the hunt for the Fallen is going to be a big part of your Chapter's identity.
Legion 5: White ScarsEdit
Jaghatai Khan and his White Scars are amongst the most fearsome and savage warriors of the Astartes. They are also well known for their love of high-speed warfare. To battle with the White Scars is to battle with a storm. They strike like lightning. The White Scars have a primal fury about them that is awe inspiring. If you make a Successor to them they may have the same apptitude for fast moving combat. Also they are a good choice for a parent Chapter if you are looking for a Chapter with more of that savage, barbaric fury to them.
Legion 6: Space WolvesEdit
As stated, Space Wolves' geneseed is by far the most unstable of all loyalist Legions and only one chapter is ever created of them, the Wolf Brothers. You can, however, expand upon Space Wolves, if you can't let go of the most impressive badasses of the Imperium. The Space Wolves are known for be somewhat feral in both appearance and combat style, so any related characters or factions will retain that trait.
Legion 7: Imperial FistsEditThe Imperial Fists. The sons of the brilliant Rogal Dorn. After the Ultramarines, the Imperial Fists are likely the most common lineage for a Chapter to have. Like the Ultramarines and their successors the Imperial Fists and their progeny tend to follow the Codex Astartes pretty closely. The trait that most commonly sets the sons of Dorn apart; is zeal. Imperial Fists and their successors tend to have an even more pronounced drive to claim glory for themselves, and to make up for any shortcoming they have. Success matter to them more than most. Thus they tend to be prolific Chapters with many honors. The Imperial Fists also have a very strong, respected reputation with the various branches of the Adeptus Terra, and thus the line of Dorn can often have politcal clout. It should be noted that the Ultramarines and the Imperial Fists as well as their successors tned to have a rivalry with one another. How friendly or hostile this rivalry is depends upon the Chapter in question.
Legion 9: Blood AngelsEditTo be a successor of the Blood Angels is to have a long history of glory, nobility and grief. The Blood Angels and their successors are often of a particularly noble spirit, and usually possess glorious service records. However any Chapter descended from the Blood Angels suffers from an ongoing struggle with the Gene-curse of Sanguinius's line. The Black Rage and the Red Thirst. Those that possess this gene-seed have to struggle daily to reign in their aggression and keep hold of their sanity. This is why the line of Sanguinius is believed by many to be cursed, and ultimately doomed. Thus if you make a Chapter of this lineage they are going to have to come to grips with the realization of a tragic fate. The Blood Angels and their successors have a naturally heightened aggression by Marine standards, and excell in close quarters combat, making them some of the most effective assault Chapters in the Imperium. If your Chapter comes from this line they are very likely to have similar organizational structures to their parent Chapter. They may possess members of the Sanguinary Guard, and will most certainly have a Death Company of some sort. While the Blood Angels and their progeny have proven themselves again to be fearsome warriors, and dedicated servants of the Emperor, their reputation has been marred by their curse. So other Imperial forces may be wary of your Chapter.
Legion 10: Iron HandsEdit
The Iron hands are known primarily for two things. First of is their obsession with technology and modifying themselves with bionics. Secondly is their strong, bitter hatred. If you were to make a successor for the Iron Hands they are very likely going to be very tech adept, and may have strong relations with the Adeptus Mechanicus. They may also be just as cold and unfriendly as their forebearers. It is thought that the Iron Hands' need to replace their flesh with metal is a side-effect of a gene flaw. If this is so then your Chapter may suffer the same compulsion.
Legion 13: UltramarinesEdit
If your Chapter is part of the lineage of Roboute Guilliman, then you are in good company. Of all Space Marine Chapters 60% make use of Ultramarine Gene-seed, making them the
most populous and successful bloodline of all Space Marines. They can be considered the "standard" for Space Marines. Ultramarine Successors tend to be strict followers of the Codex Astartes, and the line of Guilliman is infamous for its regimented nature and discipline. They are also known to have the most stable Gene-seed out of the first Founding Legions, making them excellent gene-stock. If you are worried about your Chapter being "unique", don't worry. Since the Ultramarines gene-progeny are so numerous and widespread many have diverged quite a bit from the traditions of their parent Chapter. There are even Ultramarine Successors that are Non-Codex. So don't worry your little head.
Legion 18: SalamandersEdit
The Salamanders have no known successors, though there are some that are suspected. However a consensus was reached over a debate that while no successors are named, there is no practical reason that they cannot actually have successors except for the decision of Games Workshop. Salamanders are known for two things, thier preference for flame weapons and a code of chivalry of sorts. Honour and Strength are principle teachings of the Salamanders Chaplains, and they also go out of thier way to protect those scummy mortal men and women like yourself.
Legion 19: Raven GuardEditThe Raven Guard are a Chapter that rarely have successors. They were never one of the larger Legions, and the Drop Site massacre left them undermanned. They just barely managed to recover from their losses with forbidden science when the 2nd Founding occured. The Sons of Corax are known for their sharp wits. Where other Chapter roar onto the battlefield like thunder, eager to bring terror to the foe and glory to the Emperor, the Raven Guard applies force with a calculated precision and cunning. They choose to fight smarter against the enemy rather than harder. If you were to create a Raven Guard successor they may have these traits, and would possess the pale skin and dark eyes that has resulted from the subtle mutation of their gene-seed.
- Main article: Warhammer 40k fanon:Canon Policy#Successors
Sometimes a Chapter of a later Founding is given the honor of having their gene-seed used to create a successor Chapter. This is a tremendous honor amongst the Astartes, as it singles the Chapter out for its great service and valor. Successors of such Chapter may wish to adopt their parent Chapter's traditions and fighting style, wanting to emulate their parent. After all to be given a successor is to be acknowledged as having stood out from the rest of the Astartes. On a related note, only one successor chapter may be written for one of your Chapters. As stated, the existence of a Successor Chapter in general is a major tip of the hat to one's Chapter. Most Chapters created 2nd Founding or later don't have Successors, and even the ones that do usually only have one or two.
Legions 3, 4, 8, 12, 14, 15, 16, 17, 20: Traitor LegionsEdit
- Main article: Warhammer 40k fanon:Canon Policy#Successors
There may be no successors of traitor legions so that is that.
Legions 2, 11: Lost LegionsEdit
- Main article: Warhammer 40k fanon:Canon Policy#Successors
There may be no successors of traitor legions so that is that.
So, every chapter is made part of a Founding (with the sole exception of Sons of Medusa chapter). Here is a table of Foundings that include notes about them so use it. A solid advice is that you do not state the date of Founding, even if it is canon friendly, just say the Founding, millennium (for example mid-M36) or then just write it as "of unknown Founding".
Note: The Foundings 13th-21st are crowded in small amount of time as you can see, during that time there were huge internal strife within Imperium so it is no wonder chapters were created in numbers. You could also speculate, that as a great deal of Foundings were made in M35 (eleven!) all the genestocks were rapidly used and therefore there is no Foundings in M36. Or then the chapters were so lucky there was no need to build more in M36.
|3rd||001.M32||Not much has been said about the 3rd Founding. It is the earliest Founding that one can create a Chapter in on this site, and thus many people do since they want old, honored Chapters. While there aren't many real details about this founding there are things to consider about it. There are only two Canon Chapters that have been named that are part of the 3rd Founding. The Executioner and the Flesh Eaters. Both Chapters are known for their extreme brutality and aggression. Since this Founding happened so soon after the Horus Heresy and the Great Scouring it may be that the Adeptus Terra felt they required brutal Chapters to strike fear into the Imperial populace and scare them into compliance during those hectic times. The 3rd Founding could have been used to raise "Butchers of the Emperor" that would wreak terrible slaughter on those that opposed the Imperium. Perhaps the times that they were founded in were so brutal that the Chapter of this time developed a savage culture as a result. Mind you this is never stated, so it is pure speculation, and can be completely ignored.
There are no Dark Angels descendants in this Founding (see: Codex Dark Angels 6th Edition)!
|Executioners, Charnel Guard, Marines Malevolent|
|4th||546.M32||Happened at the climax of the Beheading.||N/A|
|5th||Unstated||This Founding occured during M33.||Howling Griffons|
|6th||831.M33||Happened during the Year of Ghosts.||N/A|
|7th||Unstated||This Founding occured right before the Howling (401.M34).||N/A|
|8th||Unstated||This Founding occured in the mid-M34.
These five Foundings (8th-12th) all have one thing in common. They occured during the Nova Terra Interregnum. A time of extreme unrest and civil conflict in the Imperium when the Ur-Council of Nova Terra declared independence from the rule of the High Lord of Terra and took the whole Segementum Pacificus with them. So what can you expect from a Chapter created during one of these Foundings? You can expect them to be battle hardened. In addition to being founded during a period rife with civil conflict it was said that the Imperium Founded these Chapters out of a need to stabilize its borders. Thus Chapter of these Foundings have a good chance of being posted in or near volatile, dangerous areas that the Imperium felt they needed more firepower in.
|9th||Unstated||This Founding occured somewhere between c.500M34 and c.500M35! (See 8th)||N/A|
|10th||Unstated||This Founding occured in the mid-M35. (See 8th)||Astral Claws|
|11th||Unstated||This Founding occured during the Nova Terra Interregnum. (See 8th)||N/A|
|12th||Unstated||This Founding occured during the Nova Terra Interregnum. (See 8th)||N/A|
|13th||Unstated||The 13th Founding, aka the Dark Founding was an infamous Founding known for the fact that it was the only Founding of which almost nothing is known of. Which Chapter and how many were created during it as well as who their Genesires were was not accurately recorded, and thus the Founding and those Chapters created from it are shrouded in mystery. It is generally believed that the Inquisition intervened heavily in this Founding, and it's a good bet that some hinky stuff went on. If you make a Chapter from this Founding you can do some fun stuff with them. Your Chapter may be charged with keeping watch over a particularly dangerous secret or threat, like guarding one of the Imperium's forbidden zone like the Death Spectres. The Chapter might have been granted unique equipment or training for facing a certain enemy. They may have even undergone experimental procedures to improve their combat capabilities or grant them unusual abilities like the Exorcists did, though they wouldn't have any alterations as drastic as those of the 21st Founding. If you make a Chapter of this Founding you should capitalize on their mystery by making their Genesire unknown. This Founding is great for when you want a Chapter with close ties to the Inquisition. It should be noted however that Chapters from other Foundings may find 13th Founders untrustworthy.||Death Spectres, Exorcists|
|14th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|15th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|16th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|17th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|18th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|19th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|20th||Unstated||This Founding occured somewhere between 975-991.M35.||N/A|
|21st||991.M35||During the 21st Founding the Adeptus Mechanicus thought that they might be able to remove some of the Gene-flaws that plagued certain Chapters, and maybe even improve Space Marine Gene-seed to make even more formidable warriors. They believed that their understanding of genetics would allow them to make better Chapters, and so tampered with the blessed Gene-seed of the Astartes. Turns out they were dead wrong. An overwhelming portion of the Chapters created during this Founding developed drastic mutations. Those that didn't often suffered great calamity and misfortune. When everything was said and done good portion of this Founding was either disbanded or purged. In the eyes of the rest of the Imperium the Mechanicus, in their hubris tried to improve upon the Emperor's design, and rejiggered things they had no business jiggering with in the first place. So the Emperor cursed this whole batch of Marines, thus the name. If you were to create a Chapter from this Founding they would be part of a few, surviving Chapter that has as of yet avoided calamity or destruction. 21st Founders can have all sort of unique traits and mutations, though you have to be careful how you right them. After all gentic instability is amongst the most common grounds for Chapters to be destroyed. In addition to whatever physical differences they might have your Chapter is also likely to enjoy a feared reputation from enemies and allies alike. The drawback is that your Chapter isn't going to have a lot of friends. Remember everybody else thinks they're cursed. In their eyes it is only a matter of time before your Chapter goes rogue, devolves into grotesque mutants or falls victim to some epic disaster. Thus they aren't to keen to stand close by your Chapter's side, less they too are dragged into whatever calamity your Chapter is destined for. Many Imperial forces may refuse to fight alongside you. They are just watching and waiting for your Chapter to fall from grace, and thus you can only count on the most open-minded, reckless or desperate of forces to befriend your Chapter.||Black Dragons, Fire Hawks, Flame Falcons, Sons of Antaneus, Minotaurs, Lamenters, Blood Gorgons|
|22nd||Unstated||This Founding occured right before the Great Culling (020.M37), in early-M37.||N/A|
|23rd||Unstated||The 23rd Founding occured during a period when the Imperium was hurting for some Marine firepower. They had lost a lot of Chapters in the time previous due to the Age of Apostasy, the Cursed 21st Founding and many other tragedies. The Imperium was being pressured by its enemies and they desperately needed a new generation of battle hungry Marines to replenish the deplete ranks of the Astartes and push back the rising tide. Thus the Sentinel Founding occured. Sentinel Chapters tend to be restless, and possessed of a strong crusaders zeal. The Founding is filled with Crusade Chaptes that plunged into the battlefields of the far future almost as soon as they were created, and never stopped fighting. Thus like the Chapter of Foundings 8-12 they are likely to be battle hardened, but while those Chapters gain their experience from being posted in areas where the enemies of man attack relentlessly, the Sentinel Chapters gain their bones by taking the fight to the enemy. When there is nobody to battle they don't patrol areas of space waiting for the distress call. These Chapters go wherever the enemy is and bring them to battle. For this reason this Founding has gained respect in the eyes of their peers.||Marines Errant, Imperial Harbingers, Star Phantoms, Steel Cobras, Celestial Lions|
|24th||Unstated||This Founding occured in M39, when Age of Waning begins.||N/A|
|25th||Unstated||This Founding occured in late M40.
Your Chapter is young. So they don't have the storied history that the older Chapters have. However you should not count them out. Just because these Chapters don't have the same experience that older Chapters have doesn't mean that they are any less capable. Since they are young they will be eager to get out into the galaxy, and prove their worth to their older brothers. Plus they have chosen a great time to do it. The Imperium is facing more dangers than ever before. Chaos is gaining momentum, the Tyranids have smashed into the galaxy, and aliens that would have never dared defy the Imperium before are now brazenly striking out against the Imperium. Your new boys have their work cut out for them, but they have yet to be worn down by millenia of combat, and are likely to be flexible a less set in their ways than the older Chapters, who have long since put their trust in their time tested methods.
|Fire Angels, Star Scorpions, Omega Marines|
|26th||738.M41||See 25th Founding.||Mentor Legion|
Battle cries, famous sayings, mottoes, it is not strictly necessary for you to write a bunch of these, but they add color to your Chapter, and help make clear their philosophy and makeup.
What is your Chapter's symbol? It may be an heraldic animal, a sunburst, a random squiggle. Whatever it is, it will strike terror into the hearts of their enemies and inspire the Marines to feats of valor.
What are you Chapter's color? They could be solid, halved, quartered, or something bizarre. I suggest you go check out the Bolter and Chainsword Space Marine Painter: http://www.bolterandchainsword.com/smpbeta.php it can help give you an idea of what the colors will look like on a Marine, and you can download the pictures you make. There is a Terminator and Scout Marine painter as well. http://www.bolterandchainsword.com/tsmp.php - Terminator http://www.bolterandchainsword.com/sctp.php - Scout Marine
This has gotta be the most common canon-infringement I've seen: Mega-Bolters, laser death rays, Alien psycho-powered swords; it's like nobody's content with a simple gun any more!
While a Space Marine is still a Space Marine without a gun, it does help. Your Chapter's equipment should be consistent with their favored tactics, be they assault, skirmish, hand-to-hand, or ranged combat. The best custom equipment tends to be slightly more advanced versions of existing equipment, with reasons for how and why they were developed (or found) and why the said equipment is unique to that chapter. Also keep in mind that a lack of unique equipment can actually improve the character of your chapter as you find other reasons to make them special and this can also apply to weather they are a Codex or Non Codex chapter.
Each Chapter maintains its own fleet consisting of up to three Battle Barges and some number of Strike Cruisers and support craft.
Chapters are forbidden from having any more than three Battle Barges: any more, and you're gonna have the Inquisition, and the Navy, and all sorts of unfriendly people wanting to know exactly why the Chapter needs so many Battle Barges.
- "...For his wrath exceeds that of the Emperor himself. Indeed, my character here should be the next emperor!"
- — NO!
Who are your chapters heroes? What names ring forth like a trumpet call to call your Marines onward when all seems lost? Your Chapter's characters may be the epitome of perfection (as the Chapter sees it) or they could be rogues and scoundrels, barely-tolerated outcasts.
Whatever you do, please do not describe your characters with phrases like 'almost as mighty as a Primarch' or 'Nigh Invincible'. Okay, they're really tough, we get that; they're Space Marines. Belaboring the point will only make them look like posers.
Philosophy and MakeupEdit
The purpose of a Chapter is very simple: to kill the enemies of the Emperor, the heretics and Xenos that infest the galaxy: they are the HAMMER of the Emperor, his strong right arm, they CRUSH the enemy: that is their purpose in life.
They don't go around being nice to people;
They don't go around making alliances with Xenos;
Space Marines are not sneaky: they do not have their own private spy network, they do not go rooting out hidden cults and they do not, repeat, do NOT oversee the Inquisition (or vice versa) and go around killing all the overzealous Inquisitors who aren't nice.
So, in those lines, you can make up about the Space Marines philosophy. Are they dour and serious, or hermetic, coming out only to battle the enemies of Humanity before returning to their solitude, or do they take a great interest in the universe around them?
Every Chapter has a role they tend to fill in battle: deep penetration, pin-point assaults, jungle warfare, tunnel fighting, or they could be your simple everyday unstoppable super-soldiers. Keep in mind this section can be heavily related to their traditions and equipment.
Who are your Chapter's rivals? How do they relate to other Chapters? To the Imperial Guard, the Navy? To the Inquisition, the Adeptus Mechanicus, the High Lords of Terra? Are there any Chaos Warlords out there who have it in for them? People are often judged based on their enemies and their friends, so be sure to give you Chapter good ones!
Po' po' babyEdit
A disturbingly common theme is the 'misunderstood heroes' who are being picked on by the Inquisition/Adeptus Mechanicus/Imperial Guard/Navy/Ecclesiarchy/all of the above, and yet somehow manage to save all of humanity.
This can make an excellent story, but if it's not done very well it just comes off as whiny.
Also as a note, a worryingly common issue is peoples' misunderstanding of how much authority the Inquisition has over the Adeptus Astartes. The Inquistion has only limited authority over a Chapter, and can't seize control of chapters or declare them heretics without solid proof of heresy since space marines are so valuable and rare. For the Inquisition to have any kind of direct authority over a chapter, that chapter must be a repentant chapter. The High Lords of Terra may also grant an Inquisitor power over a chapter under special circumstances.
Moreover, there is a certain conceit that Inquisitors are never right - their pronouncements of heresy are always made because the Inquisitor is just a big bully and doesn't like the chapter. If you do want chapter-Inquisition friction, it helps to give the latter group at least a tiny bit of traction.