Jay Scott Greenspan, better known by his stage name Jason Alexander, (born September 23, 1959) is an American actor, comedian and singer, best known for his role as George Costanza on the television series Seinfeld.

He appeared with Jerry Seinfeld in "When You Wish Upon a Weinstein" in an episode of Seinfeld as his character George Costanza. He also provided the voice of Louie Anderson in "There's Something About Paulie".

Alexander appeared on the 2005 album Family Guy: Live in Vegas singing "All Cartoons are F**kin' Dicks" with the rest of the cast.