An American stand-up comedian, singer, and actor. He had several comedy albums in the 1970s, was nominated for a Best Actor in a Musical Tony Award for 1979's They're Playing Our Song, and has made a variety of TV and movie appearances, including hosting Saturday Night Live twice.

Klein has appeared in such movies as The Owl and the Pussycat, Hooper, Primary Colors, Radioland Murders, Ira and Abby, One Fine Day, Two Weeks Notice, How to Lose a Guy in 10 Days, The Last Unicorn, and The Safety of Objects. He had a recurring role in the TV drama series Sisters. In the 1970s, he hosted Saturday Night Live twice. He also appeared as a guest star in the animated series Duckman, the NBC sitcom Family Ties and on the CBS sitcom The King of Queens.

In March 2007, he once again collaborated with Adam Sandler (after appearing in Mixed Nuts) in Reign Over Me, and in September 2007 released a new DVD compilation of his eight live HBO specials, titled Robert Klein: The HBO Specials 1975–2005.