100% fannon up in here
The Feris Fratres (meaning "Wild Brethren") is a force of extremely diverse characters from throughout the Imperium who fight as a "Companion Company", or a Company of Mercenaries who use all of their earnings to further a set of objectives. The founding of the Feris Fratres dates back to 812, M38. At this time the Falcon Brothers, a loyalist Space Marine Chapter, were universally deployed to destroy Aegaron Nohennis, a Warlord of the Emperor's Children attempting to ascend to Daemonhood. The traitor lord, realizing too late that he would have no time to ascend, detonated Phosphex bombs hidden just under the surface of the planet, annihilating the entire Chapter. Only Garagael Mors and Vamion Valyreos survived, the remaining Falcon Brothers dead upon the world. Garagael would later fall to Chaos and be killed by Vamion. Vamion Valyreos recovered the Power Sword of his Chapter Master, Godbane, and now uses it as his personal weapon.
Vamion Valyreos traveled to the ruined world of Mallaeris, which had been consumed by urban sprawl and abandoned years before. Within the tombs that formed from the Hive Spires of the world, Vamion found four men; Stark, an escaped Zoat, Foggog, a Galg Mercenary, and the twin-renegade Space Marines Varius and Marius of the Lions Defiant Chapter. Vamion found himself befriending these refugees, even the xenos. Eventually Vamion and his new companions found Selkirk Daws, a Rogue Trader who agreed to take them off world in exchange for mercenary service. After a successful adventure in the Veiled Region, the Companions decided to form a mercenary Company, using Selkirk's Warrant of Trade as justification for the employment of xenos, renegades, and mutants. This was how the Ferus Fratres were created.
The Ferus Fratres number in some 4,000 strong, most of them mortal but a few of them Space Marines. Vamion Valyreos is the current "Praetor" of the Company. They fight as a single force, and are hired by almost every faction in the Galaxy. The Ferus Fratres have a simple motto "So long as we fight, we live, and so long as we live, we fight".
Vamion Valyreos -Praetor of the Ferus Fratres and sole survivor of the Falcon Brothers
Varghost the Giver -A Fallen
Stark -The last known surviving Zoat in the Galaxy
Foggog -A Galg who has a bitter memory of the Imperium
Selkirk Daws -A Rogue Trader who originally smuggled the warriors off of Mallaeris
Varius and Marius -Twin Space Marines formerly of the Lions Defiant Chapter
Syrax -A Hrud scout who's an expert at sabotage
Gox -An Ork who was implanted with the memories of a fallen Techpriest, making him hyper-intelligent