I'd on occasion wondered why the German plan to invade Russia during the Second World War was codenamed Operation Barbarossa. It doesn't feel like a very Germanic name, and my basic knowledge of Romance languages had me thinking it must mean something along the lines of Operation Redbeard. As such I'd thought it might be some kind of reference to the Red Army, but the actual answer is more interesting.
The name comes from Frederick I, also called Frederick Barbarossa, Holy Roman Emperor during the 12th century. Barbarossa was regarded as among the most charismatic leaders of his age, and tried during his reign to establish the European dominance of the Holy Roman Empire (comprised predominantly of modern-day Germany); the appeal of such his name to the Nazis is obvious. Interestingly, the plan did originally have a much more Germanic-sounding name, Operation Fritz.