The longest-running animation in the history of television and the most syndicated show in - well, history, has spawned many catchphrases in its 20 years of existence. Among them are Bart's Ay, caramba!, Mr Burns' Excellent!, Apu's Thank You! Come Again! and Ned Flander's Okilydokily, but the most endearing - or annoying - of these has to be Homer's D'oh!, which has now entered the Oxford English Dictionary albeit without the apostrophe.

D'oh! is the sound the hapless father of three makes every time he gets himself into another fine mess. One can only guess at how many times he will thus express himself throughout the 87 minutes of The Simpsons Movie, which goes on worldwide release on Friday. As fine messes - such as acts of stupidity or self-inflicted injury - are an integral part of Homer's humdrum life, there's a distinct possibility of a high D'oh! count.

The choice of the term fine mess is deliberate, because the origins of the cartoonly ejaculation lie in the Laurel & Hardy films of the 1920s and 1930s. Arguably, it should also be uttered with a Scottish accent. For although the original Simpsons script simply instructed Homer to emit an "annoyed grunt", the voice actor Dan Castellaneta, aka Homer, translated this as an elongated d'ooooooh!, taking as his inspiration the Scots actor James Finlayson.

Larbert-born Finlayson was the bald, fake moustachioed actor who appeared in 33 Laurel & Hardy films and whose trademark comic mannerisms included squinting, "double-take fade-away" head reactions and that long d'oooooh. Finlayson also starred alongside Stan Laurel in 19 films, and opposite Oliver Hardy in five, before the comic pair teamed up. Although Laurel also d'oh-ed, it was Finlayson who made it his own. The word Damn! was considered blasphemous in the era of black and white films, so Finlayson used D'oh to suggest the word without actually saying it.

According to Simpsons creator Matt Groening in a recent interview, Finlayson's d'ohs were "a slow burn", especially in films such as Me and My Pal and Our Relations. Groening felt it would be better if Castellaneta/Homer said it a bit faster to suit the timing of animation, and so it was shortened to D'oh!

"Dan knew all about Finlayson," Groening said. "He first said D'oh! in a scene in the first Krusty the Clown episode of The Simpsons where Krusty is throttling Bart and it cuts to Homer and Marge his long-suffering blue-beehived wife watching." This was in January 1989, when the show was still enjoying its third and last season as an animated short on the Tracy Ullman Show. It was next heard later on in the same year in the first stand-alone episodewhich was broadcast on the Fox network in December 1989. In this episode, Homer dresses up as Santa Claus, bumps his head and says: "Ho-ho-d'oh!".

It was over 30 years since the Flintstones had become the first animation to be aired primetime on a national network, and The Simpsons - a satirical parody of the Middle American lifestyle featuring the yellow-skinned family of Homer, Marge, Bart, Lisa and baby Maggie who live with their friends, colleagues, enemies and neighbours in the fictional town of Springfield - duly took America by storm. Its popularity was boosted by President Geoerge H W Bush's infamous comment: "We're going to strengthen the American family by making them more like the Waltons and less like the Simpsons."

Since then, Fred Flintstone's Yabadabadoo! has been clubbed into oblivion by Homer's more primeval D'oh!, which has risen to stardom in its own right. It has been adapted for several of the 400 Simpsons episodes to date. One of these is in Bart of Darkness, when Homer, while talking to an Amish man, responds: "D'oheth!"

However, the funniest D'oh! adaptation, in this writer's opinion, is in Bart Gets An Elephant. When Homer crashes the family car into a preserved deer statue, he exclaims: "D'oh!", then Lisa says "A deer!" followed by Marge, who adds: "A female deer!"

Finlayson's crucial though largely unknown contribution to the Simpsons' phenomenal success has perhaps been acknowledged after all. Why else would the Springfield Elementary school janitor, Groundskeeper Willie, be a moustachioed Scot? And a blasphemous one at that?