Raubvögel was an Elite German Sniper. He was the orchestrator of the plot to assassinate Winston Churchill.
He was a very meticulous planner and had several methods of execution planned for Churchill.
He was also very confident in his skills as a sniper, setting up a note to taunt Karl when he reached his position, though he was ultimately bested in the end.
He wore a metal mask and body armor to offer more protection. Karl claimed the mask as a trophy.
Raubvögel means "Birds of Prey" in German, which is an odd choice for a person's name. This is most probably an oversight on the developer's side and it's meant to be "Raubvogel" (without the Umlaut) instead, which would be the proper singular spelling.