Mutt and Jeff was a comic strip that ran from November 15, 1907 to 1982. It was created by Bud Fisher , though for most of its run (1932-1980), it was drawn by Al Smith . Other contributors included Ken Kling , Ed Mack , and George Breisacher .

While not the first daily comic strip, it was the first successful one and is credited with establishing the format of a six-day-a-week strip with a regular set of characters.

The strip was originally titled A. Mutt and appeared on the sports pages of the San Francisco Chronicle. Augustus Mutt was a tall rangy racetrack character, but the strip was transformed when Mutt encountered the half-pint Jeff (an inmate of an insane asylum) on March 27, 1908. On June 7, 1908. The strip moved off the sports pages and into the Hearst-owned San Francisco Examiner where it was syndicated and became a national hit.

Fisher had taken the precaution of copyrighting the strip in his own name. He became wealthy through the strip, a comic book, cartoons and reprints. He finally turned the production of the strip over to Smith in 1932, who continued to draw it until two years before its demise in 1982.

In 1910, during the silent film era, at David Horsley's Nestor Comedies in Bayonne, New Jersey, Al Christie began turning out one single reel of a "Mutt and Jeff" comedy picture every week. The operation moved to Hollywood and more than 300 animated Mutt and Jeff shorts were released, making it the longest animated series in cinema history (although Popeye has appeared in the most cartoons if television is included).

Before Smith began drawing the strip, Mack introduced a plotline featuring Mutt running for President, during the 1928 Presidential election when the same-named Governor Al Smith was a candidate. Mutt was the first cartoon character to seek the nation's highest office. (The cartoonist was not related to the candidate. Nor was Bud Fisher related to cartoonist Ham Fisher.)

A spinoff strip, Cicero's Cat , starred Desdemona, a cat that Smith originally introduced in 1933 as companion to Mutt's son Cicero.

During the 1960s, some of Smith's strips, including Cicero's Cat, were reprinted in comic book form by Harvey Comics, sometimes also featuring conventional-length stories newly drawn by Smith.

Due to the strip's popularity, "Mutt and Jeff" became idiomatic for any tall-and-short pair of men (Mutt was the tall one). The word "mutton" is used in Cockney rhyming slang as an abbreviation of "Mutt and Jeff", and stands for the word "deaf". The names were also used as codenames for a pair of World War II spies: see Mutt and Jeff (spies). The "good cop/bad cop" police interrogation tactic is also called "Mutt and Jeff".