Alexander was born Jay Scott Greenspan in Newark, NJ. While attending Boston University, Alexander gave up on his interest in becoming a magician and instead focused on theater, for which he was a natural. He left BU before his final year when he began to land paying stage work in New York City. Bit parts in the TV movie "Senior Trip!" (CBS, 1981) and the big screen slasher "The Burning" (1981) helped make ends meet, but professionally, Alexander made more headway onstage. In his Broadway debut, Alexander's commanding singing voice and endearing charisma made him a good choice to play a stage producer in the unsuccessful Stephen Sondheim musical, "Merrily We Roll Along" (1981). More work on- and off-Broadway followed, notably in Kander and Ebb's "The Rink" (1984), a musical co-starring Liza Minnelli and Chita Rivera, and Neil Simon's autobiographical play, "Broadway Bound" (1986). Meanwhile, Alexander took a few stabs at television comedy with roles in the short-lived sitcoms, "E/R" (CBS, 1984-1985) and "Everything's Relative" (CBS, 1987). In 1989, Alexander earned a Tony Award for playing multiple roles - including Tevye from "Fiddler on the Roof" and Pseudolus from "A Funny Thing Happened on the Way to the Forum" - in the Broadway revue, "Jerome Robbins' Broadway" (1989). But while his name was known in New York Theater circles, most television audiences were unfamiliar with Alexander when he hit primetime that year playing the manic, neurotic, and perennially unlucky George Costanza on "Seinfeld." The offbeat sitcom about a New York comedian and his close-knit group of minutiae-obsessed friends took awhile to establish fans, even as its observational comedy and well-developed characters were immediately embraced by critics. By the third season, however, "Seinfeld" was a top ratings grabber, an Emmy-winning series, and the water cooler show of its day. Called the "Beatles of Comedy" by Rolling Stone, the hallowed cast became irretrievably linked to one another, with the career-challenged, balding Costanza playing a major part in making the show a true pop culture phenomenon and the cornerstone of NBC's "Must-See" Thursday night lineup.When he was not going on tirades over the party faux pas of "double-dipping" chips or masquerading as architect, Art Vandelay to impress women on "Seinfeld," Alexander kept one foot in the theater world as well as made a few supporting movie appearances. In 1990, he returned to Broadway in the comedy play "Accomplice," and had a key supporting role as a sleazy lawyer who hits on Julia Roberts in the smash romantic comedy, "Pretty Woman" (1990). Launching a secondary career as a voice-over actor, Alexander lent his theater elocution to the puppet series "Dinosaurs" (ABC, 1991-93) and the cult favorite, "Duckman" (The USA Network, 1994-97). He took the lead in the sleeper "I Don't Buy Kisses Anymore" (1992) and played one of the biological parents of a child (Elijah Wood) who searches the world in search of more suitable guardians in the family flop, "North" (1994). Showcasing his stage talent for the masses, Alexander was impressively charming and tuneful as Albert in the TV remake of "Bye, Bye Birdie" (ABC, 1995). Alexander expanded his realm to include directing; first helming an episode of "Seinfeld" before going on to direct the romantic comedy "For Better or Worse" (1995), in which he co-starred with James Woods and Lolita Davidovich. He voiced Hugo in the Disney feature "The Hunchback of Notre Dame" (1996) before the broad comedy "Dunston Checks In" (1996) proved a bit of a career embarrassment. Alexander rebounded when he led the ensemble cast of "Love! Valour! Compassion!" (1997), based on Terrence McNally's Tony-winning play about a group of gay friends who spend summer holiday weekends together.In 1998, "Seinfeld" finally left the airwaves after a highly anticipated but oddly disappointing series finale in which the foursome stand trial for not being good citizens after a man is robbed and they fail to intercede. Alexander next surfaced in supporting film roles in mainstream comedies "The Adventures of Rocky and Bullwinkle" (2000) in which he played a picture-perfect, live-action version of Boris Badenov, and in the Farrelly Brothers' "Shallow Hal" (2001) as Jack Black's equally shallow pal. Looking for another television hit, Alexander took the lead in the short-lived sitcom "Bob Patterson," playing a motivational speaker who has no business advising others on how to live. Over the next few years, Alexander appeared in a number of memorable guest-starring roles (as himself) on "Seinfeld" co-creator Larry David's HBO sitcom "Curb Your Enthusiasm" (HBO, 2000-). He starred opposite Martin Short in a Los Angeles stage production of Mel Brooks' "The Producers" in 2003, and the following year, paired with Kelsey Grammar in a musical version of "A Christmas Carol" which was then adapted into a feature film.Making a second attempt to carry his own sitcom, Alexander was cast in "Listen Up" (CBS, 2004-05), playing a sportswriter, talk show host and family man who was again a slight variation on George Costanza, but surrounded by a dysfunctional wife and kids. When that show failed to connect with audiences, Alexander took on a recurring supporting role as eccentric high school principal Corleone on "Everybody Hates Chris" (UPN, 2005-06; The CW, 2006-09), and also directed a pair of episodes of the Golden Globe-nominated sitcom. Alexander lent his voice to the animated comedy "Farce of the Penguins" (2006) while remaining active on stage as director of a number of Los Angeles productions. The theater vet took over as Artistic Director of the "Reprise! Broadway's Best" series in Los Angeles in 2007. Meanwhile, he fielded guest role offers to play oddball professors and doctors on a number of primetime series, including former "Seinfeld" co-star Julia Louis-Dreyfus' successful sitcom, "The New Adventures of Old Christine" (CBS, 2006-10). In 2009, Alexander reunited with Louis-Dreyfus again, along with the rest of the "Seinfeld" principals, on "Curb Your Enthusiasm" in a storyline involving a fictitious reunion episode of the long-departed Thursday night standby. From that highly anticipated moment, Alexander went back to his many sideline gigs, helming an episode of the procedural drama "Criminal Minds" (CBS, 2005-) and appearing in the World Series of Poker, having established himself as a poker enthusiast over years of televised games. However, any "cool" status that poker brought Alexander was offset by his position as the new spokesman for the Jenny Craig diet plan in 2010.