The Old Man is a character who appears in the animated short of Adventure Time. His diamonds are stolen by ninjas near the end of the episode. Pendleton Ward said that the Old Man would make another appearance in the series, though he was set to appear in the cancelled episode "Diamond Jim," so it is possible that he will not make another appearance.
He wears khaki shorts, has a white beard, dark blue shoes, a yellow shirt with yellow orange polka-dots, and rolled-up socks similar to Finn's socks.
Gimme back my diamonds!