The Eladax Sevean was born in the strife surrounding the traitors defeat at Terra. When the Iron Warriors fled the homeworld, they were forced to abandon many of their members on the surface. Incapacitated by the physic backlash of Horus' death, thousands of Iron Warriors were slain by servants of the false emperor. A strong and capable Iron Warrior Captain, whom had long since fallen to chaos named Eladax regained consciousness and combat ability first. He managed to rally a ragged group of survivors, about 600 in total. They fought off meager White Scars assaults, losing few brothers to those probing attacks. Seeing the sky fill with the fleeing shapes of Chaotic voidships, Eladax desperately attacked one of the few remaining dropships on the ground. Slaughtering it's 300 or so defenders they lifted off and were nearly immediately heavily damaged by falling debris of a Chaotic battleship destroyed at the beginning of the battle. Heavily damaged, Eladax docked with the Conquerer, flagship of the World Eaters legion. In their Khorne inspired madness, the World Eaters refused to quit the field, and Eladax was forced to sit in the hangar grinding his teeth while the Conquerer sustained heavy damage until it finally jumped to the warp. When Angron learned that the Iron Warriors on board had fled the field, he was enraged and dumped them on a small moon orbiting an Imperial Feudal World. With 400 or so battle-brothers, they cut down the 1000 strong Imperial Army with ease. Salvaging what they could, they managed to get down to the planet where they commandeered a docked Imperial Escort and fled to the Eye of Terror. Later they learned that the planet they had been marooned on was called Sevean, and so they had their name. The Eladax Sevean. They tossed the colors of the Legion that had abandoned them, and took on the red and black.
As of the 41st Millennium, the Eladax Sevean still exist. They are 800 strong, a powerful and elite force of ancient chaos space marines of differing legions. Eladax himself was slain long ago, fighting against the Imperium during the Fifth Black Crusade.
Departure of Sevean
When the Sevean were marooned on Sevean, they encountered severe Imperial resistance. Though they encountered no loyalist Space Marines, they took heavy casualties from Imperial armored vehicles and infantry forces. Eladax led them to a docking station in Orbit of Sevean where they stole an escort that was awaiting repairs to it's port armor.
Slaughter at Kasyr Lutein
During the fifth Black Crusade, the Sevean split off from the main hoard while Abbadon slaughtered the two Space Marine chapters he had trapped. The Sevean captured several thousand Imperial Citizens and a few hundred Imperial Guardsmen. All were sacrificed to the Dark Gods.
Chaos Lord Eladax
Eladax was the founder of the Eladax Sevean, and was a great leader of the warband. Under his leadership, the cult reached almost 3000 Space Marines. A magnificent and huge force. When Eladax was slain during the Fifth Black Crusade the warband split in halves that slaughtered each other for control. One of the contending leaders, Khro'gaz Blackbane won the exchange, but only emerged with 500 Astartes. He spent the intervening six centuries building up the warband, but never equaled the greatness of Eladax.
Chaos Lord Khro'gaz Blackbane
Blackbane took over the Sevean after a brief but brutal civil war. He emerged with 500 of 3000 Space Marines, and spent the next few centuries building up the Warband, but he only managed to reach 1900 Astartes. He led some of the most disastrous defeats for the warband, eventually being overtaken by the current leader, Crumor.
The Iron Warriors
Though they were abandoned, the Sevean maintained close contact with their mother legion, coming to their aid on several notable occasions and receiving boons from them in turn each time.
Cult and culture
The Sevean favor chaos undivided, but sacrifice most of their victims to Nurgle and Khorne. Slaanesh takes the smallest cut, and Tzeench receives an intermediate amount of sacrifice.
The Sevean are a diverse group mainly specializing in boarding action to steal voidships from the Imperium. They favor close quarters weapons like flamers, chainswords, and power weapons. When they have to land, it is usually on lightly defended colony worlds, unless they are participating in a Black Crusade. They scythe through the small colonial settlements with fast, light vehicles, killing and capturing as many people as possible.
The Sevean rely mainly on Astartes coming to join their warband. These space marines are put through rigorous tests, eventually dueling at least one established brother to first blood to prove his place. Any mortals who attempt to join the warband are admitted. They are used as cannon fodder, though they must supply all their own wargear wheras an competent Astartes may be gifted with powerful weapons from Crumor's personal armory.
The Sevean do not live on Medregard, like the rest of the Iron Warriors, instead they spend most of their time raiding frontier Imperial colonies beyond the Astronomicon. Many a rogue trader has felt the sting of a chainsword as the Sevean descended upon their worlds.