Who's on first, What's on second, and I Don't Know is on third.

Abbott and Costello's "Who's On First" routine dates back to the mid-1930s; it was first performed for a national radio audience in 1938. After numerous performances of the skit, they copyrighted it in 1944. This 1945 performance from the movie The Naughty Nineties is considered their best by many.