Jason Alexander was born Jason Scott Greenspan, on September 23, 1959. His father is Alex Greenspan, and his mother is named Ruth. He has a half-sister and half-brother.
Alexander graduated in 1977 from Livingston High School in Livingston, New Jersey, where he was active in the school band. He also participated in the school plays, "Guys and Dolls", "The Odd Couple" and "Oliver". He then went to Boston University, though he left college before he graduated to pursue his acting career.
Alexander started acting professionally in New York. He performed in Stephen Sondheim's "Merrily We Roll Along", "The Rink", Neil Simon's "Broadway Bound", and "Accomplice". He took his stage last name "Alexander", from his father's first name.
Alexander won a Tony Award as Best Actor (Musical) for "Jerome Robbins' Broadway" in 1989.
He has had many movie roles, and has appeared on many TV shows and commercials, but he is best known for his role as neurotic loser George Costanza, on Seinfeld
He married Daena Title on May 31, 1981, with whom he has two sons, Gabriel and Noah.