The Exorcist reached its fiftieth anniversary last month. The seminal horror movie is credited with such cultural touchstones as gurgling pea soup, weaponised priests and a set of near-bottomless steps fatal to anyone unlucky enough tumble down them, posessed or otherwise.

Really, nobody short of Inspector Clouseau could survive a fall like that.

Which is funny because if it wasn't for the man behind The Exorcist, we wouldn’t have The Pink Panther films.

The original Panther was a surprise hit in 1963. Though director Blake Edwards’ romantic farce got a mixed reaction from the critics, the audience loved it. What was intended as a vehicle for the swave David Niven, instead introduced us to the unforgettable French police detective, Inspector Clouseau, played by the equally unforgettable, Peter Sellers.

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Sellers turned the role of a straight-forward romantic foil into a hilarious scene-stealer of such magnitude, he nicked the entire picture from Niven while the leading man was trying to steal the eponymous Pink Panther diamond.

Despite its financial success, The Pink Panther was originally regarded as a flash in the pan. While it was still in production (and its box office prospects unknown), Sellers asked Blake Edwards would he be interested in shooting his next film, an adaption of a Broadway whodunit, the script of which Sellers found uninspiring. A genius idea was hit upon: why not get a writer to replace the standard role of the investigating detective with none other than Inspector Clouseau?

Max Von Sydow in The Exorcist

Edwards knew just the man for the job.

William Peter Blatty, ex-American Air Force, appeared on the US TV game show, You Bet Your Life in 1953, winning $10,000 from none other than Groucho Marx. As a result of the windfall he devoted himself full time to writing, knocking out several well-received novels but never quite achieving huge financial success. Recognising the sharp wit of his books, Edwards hired Blatty to rewrite the entire screenplay.

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Watch: William Peter Blatty and Groucho Marx on You Bet Your Life

The result? A Shot In The Dark, now featuring not only Clouseau, but the newly-created characters of his sidekick Kato, played by Burt Kwok, and the exasperated Commissioner Dreyfus, played by Herbert Lom (a pal of Sellers since working together on Ealing’s The Ladykillers).

The film was another smash, this time both with critics and audiences. Still though, a franchise was not forthcoming. Despite the ten-year gap between A Shot In The Dark and the next Sellers-Clouseau film (let’s not count the eponymous Alan Arkin one-off), 1975’s The Return Of The Pink Panther, brought the whole cast and creative team back together.

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Watch the trailer for The Return Of The Pink Panther

With one notable exception.

A few years before the Panther’s return to the big screen, Blatty returned to writing novels. And in 1971 finally cracked it with The Exorcist. Fifty seven weeks as a bestseller, thirteen million copies sold. Despite effectively never having to work again, Blatty went on to produce the film version a couple of years later, and won an Oscar for adapting his novel into a script. But his comedy days were over.

William Peter Blatty (Pic: Getty)

Much to his disappointment, nobody ever again was willing to hire the creator of the scariest film ever made to write jokes. Which is a shame. As even in his novel, Legion, later filmed (by Blatty himself) as Exorcist III, he wrote one of the greatest put-downs ever committed to the English language (which I won’t spoil here, go read it yourself).

As for Peter Sellers, what happened to him? Well, one day back in 1980, while picking my brother and me up from school, my dad, John, had some news. "Lads, your mum will have to pick you up next week. I’m going to be doubling the Pink Panther." "You’re gonna be dressing as the Pink Panther?! Can we see?!" (I was nine, my brother six). "No. Inspector Clouseau. You remember, the 'Minkey' man?"

Peter Sellers in Dublin in 1971. He returned in 1980 to shoot a commercial.
(Pic: Independent News and Media/Getty Images)

Sellers was in Dublin to shoot a bank commercial. My dad was hired as his stand-in. My father didn’t want to bother the great Clouseau on set but planned to get his autograph at the wrap party in the Gresham a couple of weeks hence. Passers by had different ideas.

While my dad and Sellers were sitting outside at a coffee bar dressed in identical costumes. An auld fella did a double take. Luckily, he picked the right banker. Walking up to Sellers, he took out a packet of ten Major cigarettes, stuck one the mouth, one behind the ear and eight in his pocket. Ripping open the packet he thrust it in Sellers' face for a signature - "It’s yerself!"

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Watch: Peter Sellers' commercial shot in Dublin in 1980, his last appearance on film

During shooting, Sellers was relentless. "This was the first time I’d ever seen anyone use video playback on a set", my dad tells me. "He was as much a perfectionist, even though it was just an ad and not a big Hollywood movie."

My dad never did manage to get that autograph. Not feeling the best, Peter Sellers returned to London before the wrap party and died the following week of a heart attack. He was fifty four.

William Peter Blatty died in 2017 at a ripe eighty nine. His last book was a satirical novel, Demons Five, Exorcist Nothing. Those infamous steps are still there though, waiting for us all, no matter what the score. So hold fast to that handrail and laugh all the way down.

The Return Of The Pink Panther screens at the Irish Film Institute on October 25th & 27th. A re-release of the original Exorcist and its new sequel The Exorcist: Believer are in cinemas now.