Sebastian Thor
The 40k version of Martin Luther (not that one). A super-charismatic preacher who arose during the Age of Apostasy and was responsible for leading the rebellion that saw the death of Goge Vandire, the reformation of the Ecclesiarchy to prevent such an individual from ever appearing again, and the creation of the Sisters of Battle.
Perhaps one of the most widely recognized Saints of the Imperial Cult. A significant minority of Imperials believe he was an avatar of the God-Emperor himself, to the point that a faction of the Inquisition that pursues a goal of finding a way to reincarnate the Emperor is known as the Thorians. Trazyn has apparently claimed his head as a trophy for his collection.
