Lieutenant-Colonel Mikail Leonid
An Imperial Guard lieutenant-colonel at first in the book Storm of Iron, in which he outlasted Imperial Fists and every other guardsman on the fucking planet, destroyed a fuckload of geneseed to stop Honsou from getting his filthy heretic hands on it, and is actually not a Mary-Sue. Got captured by said Iron Warriors, survived torture, got taken to and survived years in the Eye of Terror until Uriel Ventris came along and broke them out, destroyed a daemonic artifact, then had the balls to stay behind with two Greater Daemons of Khorne to buy Ventris time to escape.
Balls of Motherfucking Adamantium right here. Straken could learn something.