It’s Spike Milligan’s 100th birthday on Monday. He won’t be around in person, but it’s an excuse to celebrate again how he departed with such a great punchline. Inscribed in Irish on his headstone is “Dúirt mé leat go raibh mé breoite” (I told you I was ill).

Milligan’s influence was and is inestimable. He blueprinted the crazy world of Monty Python, with John Cleese calling him “the Great God to all of us”. Dubbing him “the Godfather of alternative comedy”, Eddie Izzard said: “From his unchained mind came forth ideas that had no boundaries.” The Beatles could recite his sketches by heart.

Born in Raj India to an army captain in 1918, young Spike was a bad fit in a buttoned-down Imperial world and he absorbed his dad’s Irishness with glee as a licence to poke fun. At 21, he found himself fighting in the British army he’d despised since childhood. His war experiences in North Africa brought him in touch with future Goon Harry Secombe, and provided comic fuel for his 1970s bestsellers including Adolf Hitler: My Part in His Downfall and Mussolini: His Part in My Downfall.

He “wandered around” London as a jazz musician after the war, rekindling his friendship with Secombe, and making a new funnyman friend, Peter Sellers. Sellers and Secombe began getting occasional sketch slots with the BBC and Spike started writing for the pair. A hesitant BBC gave The Goon Show a tentative airing in 1951, and comedy would never be the same again.

Wireless audiences had heard surreal shows before – with no visuals to rein in the imagination, the medium is a place where anything can go – but Milligan took it to far-out places that no-one had ever before visited. By dint of his genius, the bulk of the writing fell on Spike, who became enslaved and broken by the demands of turning out 26 radio shows a year for nine increasingly turbulent years.

Perhaps his best-loved radio character was Eccles, a loveable innocent, who asked nothing more from life than for marshmallow clouds wafting across blue skies and everyone to be filled with peace, love and understanding. Think Forrest Gump, only funny. One collaborator ventured that Eccles was Spike’s id, that nook of the personality that houses our most basic instincts. He suggested that Milligan’s id just wanted to be left alone, playing happily in his world of make believe. But the real world of deadlines, money, fame and family kept rudely intruding and Spike couldn’t handle it.

He finally snapped in 1960, calling a halt to a phenomenon that had spread to hit stage shows and chart records. But there had been many snaps before that, and his volatility, unreliability and wild mood swings had caused huge strains with Sellers, Secombe and their BBC paymasters. The Goons fans only became aware of Spike’s behind-the-scenes tantrums when he had a breakdown in the middle of a stage show, yelling “you hate me, don’t you?” at the audience before storming off. Show over.

But when The Goon Show itself was finally over, Spike found that instead of freeing himself from his demons, he’d simply given them more headspace to mess with. “I was out of work,” he said. “My marriage ended because I’d had a terrible nervous breakdown – two, three, four, five nervous breakdowns, one after other. The Goon Show did it. That’s why they were so good.”

Good as they were, the BBC considered him toxic. The 1960s was a difficult decade where he found himself scraping around for work, both because of his reputation as difficult to work with, and because he was difficult to slot into any existing format.

In 1969, he began a comeback with the revolutionary TV show Q5 which blazed a path for Monty Python’s Flying Circus which aired shortly after. John Cleese said: “Shows prepare the way for other shows, and sometimes shows that make genuine breakthroughs are missed. Spike Milligan’s Q5 was missed. When we first saw Q5 we were very depressed because we thought it was what we wanted to do and Milligan was doing it brilliantly. But nobody really noticed Q5.”