George Louis Costanza (b. April 1959) is a fictional character on the United States-based television sitcom Seinfeld (1989-1998), played by Jason Alexander. He has variously been described as a "short, stocky, slow-witted, bald man" (by Elaine Marie Benes and himself), "Lord of the Idiots" (by Costanza himself), and as "the greatest sitcom character of all time".

George is neurotic, self-loathing, and dominated by his parents, Frank and Estelle. He has been best friends with Jerry Seinfeld since their middle school years.

George exhibits a number of negative character traits, among them stinginess, dishonesty, insecurity, and neurosis. Many of these traits form the basis for his involvement in various plots, schemes, and awkward social encounters. Episode plots frequently feature George manufacturing elaborate deceptions at work or in his relationships in order to gain or maintain some small or imagined advantage. George appears in every single episode except for "The Pen" in the third season.