20. Martin Sheen

Character: The 'real' Principal Skinner

Episode: 'The Principal And The Pauper', Season 9 ('97-'98)

According to producer Josh Weinstein, Sheen was chosen for the role of rigid military man and Vietnam vet Seymour Skinner because of his work as a scuzzy renegade-hunter in Apocalypse Now.

The actor aced his part as the prodigal disciplinarian, but the episode itself fared less well – it’s often held up as the first sign that the show's golden age was coming to an end.

19. James Woods

Character: Himself, researching a role at the Kwik-e Mart

Episode: 'Homer And Apu', Season 5 ('93-'94)

Woods was on a shortlist of actors that producer David Mirkin was desperate to feature on the show. When first-choice Michael Caine turned down a chance to appear as an actor preparing for an upcoming role, the script was rewritten for JW.

On top of his excellent ad-lib skills, the crew remember Woods for his habit of artful hesitating (all part of his regular anxious-menace schtick) which made his animated character seem more realistic.

18. Kirk Douglas

Character: Chester J. Jampwick, dispossessed Itchy & Scratchy creator

Episode: 'The Day The Violence Died', Season 7 ('95-'96)

Douglas wasn’t the first choice for grizzled down-and-out – and Itchy & Scratchy creator – Chester J Lampwick. That was Prizzi's Honour star William Hickey, who the producers described as "famous for being a grouchy, mean old man".

But Douglas could hardly have been grouchier. He refused to wear the headphones during recording as they hurt his ears (meaning he couldn’t hear direction from outside the booth) and refused to do more than two takes per line.