Alexander kept busy, though, returning frequently to the theater and racking up small movie roles in Peter Weir's "The Mosquito Coast" (1986) and Adrian Lyne's "Jacob's Ladder" (1990). "Seinfeld" and his Tony Award-winning turn in a variety of roles (including Tevye the milkman 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) really established him. Alexander's key supporting role as a sleazy lawyer in the smash "Pretty Woman" (1990) finally cracked the feature film barrier as well.
Despite his less-than-prepossessing appearance, Alexander has been one of the busiest actors on the large and small screens. He played the lead in the sleeper "I Don't Buy Kisses Anymore" (1992) and appeared as one of the biological parents in "North" (1994). The plum role of George Costanza on "Seinfeld" allowed Alexander not only his greatest career exposure but also a superb showcase for his considerable comedic talents, ranging from the playing of broad physical comedy to embodying basic yuppie idiosyncrasies of the 90s. He was also an impressively charming and tuneful Albert in the TV remake of "Bye, Bye Birdie" (ABC, 1995), played a hotel manager in "Dunston Checks In" and a doomed anti-environmentalist in the dark comedy "The Last Supper" (both 1996). The following year, he led an ensemble cast in "Love! Valour! Compassion!", based on Terrence McNally's Tony-winning play about a group of gay friends who spend summer holiday weekends together.
Alexander has also found a secondary career as a voice actor, beginning with the puppet series "Dinosaurs" (ABC, 1991-1993). He has provided the vocals for the maniacally devilish title character of USA Network's popular and clever animated series "Duckman" (1994-97), as well as the gargoyle Hugo in the Disney feature "The Hunchback of Notre Dame" (1996) and the evil Catbert in the anmaited series version of the comic strip "Dilbert" (1999-2000).
Alexander moved behind the cameras to make his directorial debut with a 1993 episode of "Seinfeld" and has thus far gone on to direct the romantic comedy "For Better or Worse" (1995), in which he co-starred with James Woods and Lolita Davidovich. His most critically acclaimed project was the indie feature "Just Looking" (2000), about a 1950s teen in Queens who becomes preoccupied with peeping on his comely neighbor (who has a penchant for appearing in her window in lingerie) only to learn to respect her as a person. Although Alexander remained behind the cameras for that film, he remained a visible presence in Hollywood in films such as "The Adventures of Rocky and Bullwinkle" (2000) in which he played a picture-perfect live-action version of Boris Badenov, the heavy-accented villain from the fabled carton series; and in the Farrelly Brothers' "Shallow Hal" (2001) as Jack Black's equally shallow pal. He also returned to television as the lead in the sit-com "Bob Patterson" (2001), playing a motivational speaker (though short-lived, the show afforded Alexander -- a die-hard "Star Trek" fan - to work with his acting idol William Shatner) and memorably gueste-starred as himself on "Seinfeld" co-creator Larry David's HBO sit-com "Curb Your Enthusiasm" in 2001. He also maintained a high-profile in a long-running series of commercial pitches for Kentucky Fried Chicken.
Alexander returned to series television as the star of "Listen Up" (CBS, 2004 - ), playing sportswriter, talk show host and family man Tony Kleinman, a slight variation on George Costanza surrounded by a dysfunctional wife-and-kids clan.