Iron Man is a song originally by Black Sabbath that is hummed by Otto in The Otto Show. The song was later sung by Nelson in The President Wore Pearls when he attempts to win back some favor to his opponent, Lisa, after she sang "Don't Vote For Me, Kids of Springfield".
Lyrics
Nelson: Hey, I have a song.
I am Iron Man!
Do-do-do-do-do-do-do; Vote for me!
Nah, screw it.