I have a suspicion that a lot of us are tragically lacking in a steady group to game with. Being the creative lot that we all assuredly are, I bet we have some character concepts that haven't seen proper play. If we can't use them yet, than at least they can see some love here.

an Unaligned Apostate as a fallen Inquisitor, condemned for his heretical studies into some mystery; likely investigation into using sorcery to predict the movement of the Tyrant Star. He would be outcast, but still have his rosette. Pour points into his Charm and Deceive, so that he could pretend to be a legitimate Inquisitor still and get his way with Imperials. Most people would be too afraid to investigate.

He would explain the party away as well. Any sort of eccentric tech-priest, blood-crazed killer, or mad psyker could easily pass as part of a standard retinue. Even the Chaos Marines could be explained away as a personal bodyguard or pretending to be Deathwatch.

His motivation would likely just be to solve the mystery he got kicked out for. Hell, he might try to bargain his way back into good graces with the Inquisition.

An Idolitrex magi who seeks to unlock the secrets of q'sal's deamon engines so he can make his own. His goal is to take both of the forges in the hallows and use them to launch a mechanical black crusade into the imperium.

A khorne deadicated fallen apothecary that turns anyone who he operates on into a combat drug adicted killing machine.

A chosen turned to canabalism who's preffered method of killing is jump pack and modified harpoon gun.

A frost father who was captured by the dark eldar to fight in thier arena. He faught his way out leading a revolt and is now back in the screaming vortex, after having explored and learned the ways of the webway, planning its subjugation.

A q'sal sorceror who changes his aleigence to nurgle and begins spreading fire and plague in his wake as a nuglite pyromancer.

An apotate who is a pirate specializing in stealing ships right out from under thier owners, and flying them away to the breaking yard.

A khorne dedicated heretek who takes the skulls of his enemies and turns them into servoskulls armed with chainblades, hand flamers, and other nasty stuff. He acts very much like megamind with his minion and the little flaoting bots.

I have several.

The first is Lorvin, an Alpha Legion Sorcerer with a mutated lightning claw and a grudge against the Black Ships he was stolen from. The claw was a 'gift' from his former master intended to kill or at least fatally mutate him. He managed to control and confine the mutation to his arm and now uses the living extention as a channel for the warp. This was the first character I created for BC. He's intended to be the stereotypical conniving sorcerer and is quite arrogant. He will not want to lead the group per se, but he would manipulate it to his own ends.

The second doesn't have a name that I can remember, but he is a former Cadian Kasrkin. Humiliation and promises of revenge (fulfilled) drew him to Chaos and he hasn't yet looked back. His specialty is infiltration and sabatoge with a particular focus on silent kills in both hand to hand combat and from extreme range. I wanted a stealth/sniper character here and I think it worked out fairly well, at least on paper. Despite his focus he is also adept at less stealthy combat as hes equiped with carapace armor and standard bolter in addition to his other weapons.

I've also forgotten the last character's name, except that it included Hellbreaker. This is an Astartes warlord of the Night Lords. One of the elite Atramentar, Night Lord Terminators, who managed to come away clean from the death of Konrad Curze and the sundering of the Legion with command of a Strike Cruiser and the facilities to create some new warriors of the Legion. Limited resources in both man power and materiel prevent him from achieving his goals however. He relies on his personal retinue of Atramentar guards and the power of his cruiser to win against enemies of both the Imperium and Chaos, raiding and siezing resources from more powerful targets. He has two great mutations. The first has melded his armor into his flesh and vice versa. He no longer eats or breathes and what was the wreckage of his helmet has melded his face into a fanged death mask. Wounds cause him to bleed flame and oily warp stuff and his autocannon arm is now inseperable from his body, firing shards of metallic bone. His melee weapon is a Pre-Imperial relic maul dubbed the Hellbreaker, from which he takes his name.

This last character isn't intended to be a PC. He's an adversarial GM character that commands the ship the PCs are based on. They are nominally part of his small warband and for the most part do his bidding, at least on the surface.

I've got one or two as well.

Dark Angel Fallen hellbent on destroying the Lion and converting the Dark Legion and their successors to the Dark Gods

Black Templar fallen to Khorne

Nurglitch Apostate who thinks that by killiing all living things he is essentially delivering them from the suffering of life

Hammer of Dorne traitor who gleefully quotes the Codex Astartes in service to Chaos

Slaaneshi Apostate who thinks that the honest evil of Chaos is superior to the false virtues of the corrupt Imperium (I did get to play this one a little, but not nearly enough)