Walter John Matthau (October 1, 1920 – July 1, 2000) was an American actor best known for his role as Oscar Madison in The Odd Couple and his frequent collaborations with Odd Couple star Jack Lemmon, as well as his role as Coach Buttermaker in the 1976 film The Bad News Bears.

Matthau was born in New York City's Lower East Side on October 1, 1920, the son of Jewish immigrants Rose (née Berolsky), who was born in Lithuania and worked in a sweatshop, and Milton (Melos) Matthau, an electrician and peddler who was a native of Kiev. His original surname is often shown as Matuschanskayasky, but this is not true (see Matuschanskayasky below for a detailed discussion). As a young boy, Walter attended a Jewish non-profit sleepaway camp, Tranquility Camp, where he first began acting in the shows the camp would stage on Saturday nights.

During World War II Matthau served in the U.S. Army Air Forces with the Eighth Air Force in England as a B-24 Liberator radioman-gunner, in the same 453rd Bombardment Group as James Stewart. He reached the rank of staff sergeant and became interested in acting. He took classes in acting at the Dramatic Workshop of The New School in New York with the influential German director Erwin Piscator. He often joked that his best early review came in a play where he posed as a derelict. One reviewer said, "The others just looked like actors in make-up, Walter Matthau really looks like a skid row bum!" Matthau was a respected stage actor for years in such fare as Will Success Spoil Rock Hunter? and A Shot in the Dark. He won the 1962 Tony Award for Best Featured Actor in a play.