A natural element of the 40K setting is the Inquisition, a kind of 41st millennium NKVD, or early KGB. Trouble is, inquisitors aren't always as weird as they could be given their reach and the wide-ranging role they have, and their recent codex isn't what we might have expected of any post-RT approach, or even a sixth edition version of the institution.
So this will be an occasional series just for inspiration, adapting some homebrew ideas for rules-light roleplaying to suit the mainstream wargame, but for no edition in particular.
Inquisitor Badnut, Xenocog
Struck by a shokk attack gun in the depths of Bea IV, Inquisitor Mercutio Rex found himself with all or part of a snotling literally on the brain. Initially believing himself possessed, but failing by apparently freak chance to take his own life, he came to accept his debilitating fate as the will of the Emperor and a gift in the struggle, refusing surgery and turning his training to communion with the creature. The ceaseless scratchings, whispers and roars have lent the inquisitor a knowledge of the Orkoid mind and allowed him in the years since to usurp the overlordship of multiple warbands, gaining great fame as a warboss while turning base greenskin drives to the work of the Emperor as well as Gork and Mork, for he acknowledges their power too, and invokes them. In the meantime reproductive spores have passed into Badnut's bloodstream and proven mutagenic, enhancing his constitution and improving his luck still further. His former colleagues are divided in their counsels. Is not the Ork a mighty ally? Perhaps by this means may the green tide finally be turned..? And all the while the spores which escape in his breath, perspiration and, yes, his foul soils sow the seeds of the Waaagh! in the very highest of imperial inner sancta...
Possible wargame rules, various editions: +1 T, but -2 Cl or -1 Ld; may take up to 75% Ork allies, or Orks as battle brothers, with Badnut and any retinue affected by the Waaagh!
I'll post more as I write them up. In the meantime, take a look at the grimdarkling detail project: Lasgunpacker has a massive 1, 2, 3, 5, 7, 800 options to my relatively poor 400.