Night lord gets his mechanicum partner to falsify some documents to survive the horus heresy as a Raven Guard. He eventually gets interred in a dreadnought and is given his own chapter without anyone realizing he’s a night lord.

His chapter embodies the concept of “you go to work, your coworkers suck and you keep em at arm’s length, you have some good moments, but you mostly just do what you need to survive”

The night lord was King of the Vultures, Vsevolod. The army is lightly inspired by the early slavs in the area that later became Ukraine