Who's on First? is a vaudevillecomedy routine made most famous by Abbott and Costello. In Abbott and Costello's version, the premise of the routine is that Abbott is identifying the players on a baseball team to Costello, but their names and nicknames can be interpreted as non-responsive answers to Costello's questions. In this context, the first baseman is named "Who"; thus, the utterance "Who's on first" is ambiguous between the question ("which person is the first baseman?") and the answer ("The name of the first baseman is 'Who'").