Frank Fontaine (19 April 1920 – 4 August 1978) was an American comedian and singer.

Born in Cambridge, Massachusetts, he is best known for his appearances on television shows of the 1950s and 1960s, including The Jackie Gleason Show, The Jack Benny Show, and The Tonight Show.

One of his earliest appearances was on the radio show, The Jack Benny Program. During an episode which aired on April 16, 1950, Fontaine played a bum (named "John L. C. Silvoney") who asked Benny for a dime for a cup of coffee. The smallest coin Benny had to offer was a fifty-cent piece, so he gave it to him. The story Benny told about this event became a running gag during later shows. Fontaine's goofy laugh and other voice mannerisms made a hit with the audience, and Benny brought him back for several more radio shows between 1950 and 1952. He also later appeared in several of Benny's televisions shows.

On the Jackie Gleason show, he played the character Crazy Guggenheim during Gleason's "Joe The Bartender" skits. His trademark was a bug-eyed grin, the same silly laugh he did on Jack Benny's radio show, and a surprisingly good singing voice. He later released an album Songs I Sing on the Jackie Gleason Show that climbed to number one on the Billboard magazine Album Charts in 1962.

Stan Freberg's voice characterization for Pete Puma in a 1952 cartoon was based on Fontaine's character voice. Fontaine received mention in satirist Tom Lehrer's 1965 song "National Brotherhood Week", from the album That Was the Year That Was. In the live show, Lehrer mentioned National Make-Fun-of-the-Handicapped Week, "Which Frank Fontaine and Jerry Lewis are in charge of, as you know." He also was to have played the voice of Rocky the Rhino in Walt Disney's The Jungle Book until Disney cut the beast from the picture.

Fontaine died in Spokane, Washington from a heart attack, at the age of 58.