I'll start with Cesare Borgia (above), a violent psychopath whose senseless wars of conquest helped to undermine the Italian Renaissance. Orson Welles played him in a film called "Prince of Foxes" which I highly recommend.
His was an interesting face, no? Some contemprary painters patterend their depictions of Christ on him.
By the way, Hitler certainly deserves a high place in this rogues gallery but I left him out because I couldn't find a suitable picture. Every photo of him has already been seen a gazillion times.