History's Greatest Villains is Zapp Brannigan's label for the personalities of Attila the Hun, Evil Lincoln, Jack the Ripper, and Professor Moriarty.
During an incident with the holo-shed upon the Nimbus, these figures came alive and caused mayhem on the bridge.
Zapp Brannigan sent them afloat in outer space when he shot a hole in the hull, despite Attila the Hun's concerns.