Sgt. Mark IV has been accused, iirc, of stealing work and claiming it as his own, which was used as the basis of Brutal Doom, a really long time ago. I've never seen any evidence for this, nor have I looked for it. Considering the amount of work he did put in BD himself since then, it can't have been more than a few percent of the product we see today. They say he's an asshole, although I've never spoken to him. I can imagine he has little patience for whining little cunts, regardless of whether that whining was deserved or not.
Now whether you believe he's literally Hitler or not, one thing's for sure. BD is really fucking cool and this whole war should have just stayed between Sgt. Mark IV and whoever he may or may not have stolen anything from. It's none of my business, in any case.