The third baseman on Abbot & Costello's baseball team in St. Louis.
Costello: If I mentioned the third baseman's name, who did I say's playing third?
Abbot: No, Who's playing first.
Costello: Stay off of first, will ya? What's the guy's name on third base.
Abbot: No, What is on second.
Costello: I'm not asking you "who's on second?"
Abbot: Who's on first!
Costello: I don't know
Both in unison: THIRD BASE!!!!!!!!!