Emperor Akihito is the Emperor of Japan.
History
When the Simpsons went to Japan for their vacation, Homer and the rest of the family went to see a Sumo Wrestling match under Lisa's suggestion. After defeating a Sumo Wrestler in a fight over a pretzel, Emperor Akihito congratulated Homer and introduced himself with his bodyguards nearby. Unfortunately for him, Homer, under the mistaken impression that he was a wrestler, leered into his face and said "Yeah, and I'm Clobbersaurus" and then picked him up, spun him around in a wrestling maneuver, and hurled him into a bin of worn mawashi, much to the bodyguards horror and to the spectators indignation. Homer was arrested shortly thereafter.
Trivia
This isn't the last time Homer foolishly and unknowingly assaulted a major foreign political figure during a family vacation and had to pay the legal consequences: He later crashes into Queen Elizabeth II's carriage in The Regina Monologues, an action that nearly got him executed.
