Alexander didn't immediately find the same level of success after "Seinfeld."
His first project after the show ended was the ABC sitcom "Bob Patterson" which only aired five episodes. He was also on the short-lived CBS sitcom "Listen Up!"
Over the years he continued to make appearances on television with roles on episodes of NBC's "Friends," UPN's "Star Trek: Voyager," Fox's "Malcolm in the Middle," USA Network's "Monk," and CBS's "Criminal Minds."
He returned to Broadway as the artistic director of Los Angeles' Reprise Theatre Company from 2007 to 2013.
Alexander also appeared on live-stage shows including "The Producers" (2003) opposite Martin Short, "A Christmas Carol" (2004) with Kelsey Grammer, Broadway's "Fish in the Dark" (2015), and "The Portuguese Kid" (2017).
Until 2020, Alexander also voiced Sy Borgman on Warner Bro's animated television series "Harley Quinn."
Some of his recent work includes cameos on Amazon Prime's "The Marvelous Mrs. Maisel" as Asher Friedman and as Gene Lundy on CBS's "Young Sheldon." He also still performs onstage, most recently starring in the comedy "Judgement Day" at Chicago Shakespeare Theater.