Bronislaw Czevak

Bronislaw Czevak is an (incredibly elderly) Inquisitor of the Ordo Xenos who ironically is one of the very few not-Eldar to have ever visited the Black Library. As a result of this, he's considered one of the foremost experts on Eldar relations, and thus a renegade to the Imperium of Man at large despite his continuing loyalty.

How He Got In

It's not like Czevak just wandered in there, after all. See, in his 400+ years as a member of the Inquisition, he'd managed to make some contacts with the leaders of Craftworld Iyanden before it got eaten. Since he managed to become friends with a farseer, he got invited to the craftworld and had a whole trip: Harlequin show, explanation about wraithguard and soulstones, and (unlikely) some night-time accompaniment. As soon as he came back, he'd decided that what had to happen was that the Emperor had to get his soul out of the thing sitting on a giant seat and into something better. His colleagues didn't take to this too well, considering heresy, even for a Resurrectionist.

Then came Darcturus. He'd gone there to look for a broken craftworld and to see if he could find the giant shrine to Khaine and figure out how an Avatar woke up. Upon finding it, the Deathwatch Kill Team that had been accompanying him decided to put him and his team under arrest and ordered that the shrine be blasted from orbit. However, guns started firing, bullets started flying, and a bundle of killer elf clowns just showed up to the rescue of the old man. Some time later, he was invited to finally visit the Black Library so he could study chaos and make sure Ahriman never got in. So he read a fuckton of books about how humanity interacted with the warp. At some point, he somehow managed to turn some of those body wrinkles into brain wrinkles and decided to get out.

His return, while controversial, was short-lived as he then got abducted by none other than Azhek Ahriman, demanding answers as to how to get into the library. The interrogation that ensued revealed an obscene lot of things except where the library was hidden. Not by any feat of sheer willpower, though, because that would make the best sorcerer in the universe look like a pansy - it turned out that the Black Library placed mental locks on him to prevent those secrets from coming out. Which then broke once he figured out how to torture the old man just the right way to undo the locks. At this point, more harlequins bailed him out and locked him up in the library...as an exhibit. Czevak spent this time just continuing his studies and reading more things while pondering what his fate was.

The Ritual

He was bailed out by the child of his farseer friend, who gifted him with a map of the webway. Now he was chased by not only Ahriman, pissed that his best lead had slipped through his ceramite-plated fingers, but also by the harlequins who refused to let those secrets get out. The old inquisitor eventually managed to leave the webway and went straight into a vessel commanded by his old understudy-turned-inquisitor. Czevak wanted to hunt down a daemon in the Eye of Terror, but was forcibly convinced to go to an inquisitorial fortress in the most indirect way possible. With webway portals. He eventually got out after robbing the fortress of a super-null embryo, which he had plans for in the Eye of Terror.

That plan? Go find where the daemon was being resurrected, go in, get Ahriman to mind-jack him into giving him the map and instead hand over the null-remains, which killed two greater daemons and burned Ahriman out a bit. He fled and was cornered again by the clowns, which he then foiled by using the map (made from the skin of a Sister of Silence) to mindfuck the Shadowseer to death and warned the library that he wasn't going anywhere while he still had enemies of man to fight.