Mona Simpson (The Simpsons) in the context of "Lisa Simpson"

"D'oh!" (/doʊʔ/ ) is the most famous catchphrase used by the fictional character Homer Simpson, from The Simpsons, an animated sitcom. It is an exclamation typically used after Homer injures himself, realizes that he has done something foolish, or when something bad has happened or is about to happen to him. All his prominent blood relations—son Bart, daughters Lisa and Maggie, his father, his mother and half-brother—have also been heard to use it themselves in similar circumstances. On a few occasions, Homer's wife Marge and characters outside the family such as Mr. Burns and Sideshow Bob have also used this phrase.

In 2006, "d'oh!" was listed as number six on TV Land's list of the 100 greatest television catchphrases. The spoken word "d'oh" is claimed as a sound trademark by the owner of The Simpsons, 20th Century Studios. Since 2001, the word "doh" has appeared in the Oxford English Dictionary, without the apostrophe. Early recorded usages of the sound "d'oh" are in numerous episodes of the BBC Radio series It's That Man Again between 1945 and 1949, but the OxfordWords blog notes "Homer was responsible for popularizing it as an exclamation of frustration." The term also appeared in an early issue of Mad comics, with a different spelling but the same meaning, in issue 8 (December 1953 – January 1954); in a one-page story by Harvey Kurtzman entitled "Hey Look!", a man seeking peace and quiet suddenly hears a loud radio and, grimacing, says, "D-oooh – the neighbors [sic] radio!!"

The Simpson family are the titular main characters featured in the animated television series The Simpsons. The Simpsons are a nuclear family consisting of married couple Homer and Marge and their three children, Bart, Lisa, and Maggie. They live at 742 Evergreen Terrace in the fictional town of Springfield, United States. They were created by cartoonist Matt Groening, who conceived the characters after his own family members, substituting "Bart" for his own name. The family debuted on Fox on April 19, 1987, in The Tracey Ullman Show short "Good Night" and were later spun off into their own series, which debuted on Fox in the United States on December 17, 1989, and started airing in Winter 1990.

Alongside the five main family members are Homer's father Abraham "Grampa" Simpson, Marge's sisters Patty and Selma Bouvier, and the family's two pets, Santa's Little Helper and Snowball II; all of them feature in major supporting roles. Other, less prominent relatives that appear infrequently include Marge's mother Jacqueline Bouvier, Homer's mother Mona Simpson, his half-brother Herb Powell and minor relatives.