Relictors
The Relictors (formerly called the Fire Claws) are a renegade Space Marine Chapter in Warhammer 40k. Most of their fluff was written in the lead-up to the 13th Black Crusade summer campaign... and then barely a mention since then.
Essentially, they're like the radical Inquisitors (Xanthites, in particular) that believe they can fight Chaos with Chaos. Indeed, their current name (Relictors) comes from their unhealthy obsession with Chaos-related artefacts and weapons. Of course, why a normal bolter didn't suffice is unclear. They were put on such a path by a rogue Inquisitor who introduced the Marines to his views; over time, the two forces hoarded an impressive amount of Chaotic bling. It was not to last, however; the Inquisition was hardly impressed by what they saw as dangerous heresy, killing their colleague and sending the Chapter on a penance crusade.
However, it seems the Relictors didn't intend to abandon their ways at all and slowly began to acquire more Chaos artefacts. The Inquisition began to note rumours of the Chapter but didn't do anything, until the Relictors attacked an Inquisitorial archive and nicked some Chaos artefacts. At that point, any notion of restraint left the Inquisitors' heads and they sent the Grey Knights against the Chapter's orbital fortress monastery. While the Chapter was badly mauled, it is rumoured a few hundred Battle-Brothers survived and are in hiding... leaving the door open for you to collect your very own horde of them!
After this awesome fluff, released primarily through White Dwarf, we haven't heard much about them. It could be that Games Workshop has decided that their story is done and nothing more needs to be said. Still, they appear every so often in the background; for instance, Be'lakor leads a group of them into an ambush in his new Dataslate for 40k.
Come to think of it, they're basically Blood Ravens with extra heresy.