The thoughts of Philip K. Dick have squirmed their way into popular consciousness in the four decades since his death. His stories have been revived in a slew of film and TV adaptations; Minority ReportA Scanner DarklyTotal RecallThe Man In The High Castle and, most famously, Blade Runner, which have helped confirm Dick’s reputation as one of science fiction’s most intriguing philosophers.

Despite his posthumous success, Dick wasn’t looking for fame. Instead his writing was a way of self-medicating, of unravelling the knots of his troubled psyche. He plumbed the depths of a rich and disturbing imagination to explore his fears and unreliable perceptions. And out of his increasingly schizophrenic mind poured hallucinatory worlds and metaphysical musings by the bucketload.

What is real and what is fake was Dick’s major preoccupation. Frequently in his novels the protagonist begins to realise the world they’ve taken for granted isn’t as it seems – that reality as they know it is a veil and that something complex and terrifying is lurking behind it. His works ask us, with wry humour, whether we can we trust our identities, memories and experiences.

Dick’s novels often feel like explorations. He would start writing with a premise in mind and have little idea where it was going to take him. Like many of those embedded in the counterculture of 1960s California, Dick embarked on drug-induced voyages to try to discern the nature of reality. But few brought back accounts that were as cogent or poignant.

Dick’s terrestrial life was a chaotic mess. He was married five times. His mother paid his rent until he was in his forties. At one point he was so poor he started eating dog food, though perhaps with one eye on the melodrama of the impoverished creative. His apartment hosted a revolving cast of dope fiends and speed freaks. At his peak, he consumed a thousand amphetamine pills a month, helping to explain his blistering productivity, churning out 44 novels and more than 100 short stories over his 30-year career.

The death of his twin sister shortly after birth had a profound effect on Dick and his work. Throughout his life he was tormented by the idea that it was actually he who had died and that his entire existence was a waking death. In several of his stories a dark-haired girl appears and reveals to the protagonist that their world is an illusion before slipping away. This is Jane, his lost half, who he continued to search for all his life.

As a teenager Dick read Proust, Joyce and Jung alongside all the science fiction he could lay his hands on. In the early 1950s he started to eke out a measly living writing short stories for pulp magazines. His big break came in 1963 when he won the prestigious Hugo Award for The Man In The High Castle, a painstakingly researched counterfactual history imagining that the Nazis had won the war, with an existential twist at its heart.

Over the next five years Dick produced a staggering 16 novels. They are some of his best works, combining prescient reflections on global surveillance, alternate realities and human replicas with visceral worlds and punchy plots. In The Three Stigmata of Palmer Eldridge Martian colonisers escape their miserable existence by taking drugs which turn them into dolls. Ubik is set in a future world in which psychic powers are harnessed for corporate espionage. And in The Penultimate Truth, humanity cowers underground believing the Earth’s surface has been destroyed by nuclear war when in fact the world is intact and inhabited by an elite living on vast estates.

But as the 1960s came to an end and the hippie dream dissolved, Dick suffered a nervous breakdown. His drug use spiralled and his already tenuous grip on reality loosened. The Soviet science fiction writer Stanislaw Lem, who was dismissive of what he saw as the tendency of American sci-fi to recreate cowboy stories in space, wrote an essay entitled “Philip K. Dick: A Visionary Among the Charlatans”. Dick didn’t repay the compliment, claiming that Lem did not exist, that he was a fabrication by a team of KGB writers whose job, through the medium of obscure science fiction, was to spread anti-American propaganda.

Dick’s amphetamine abuse inspired A Scanner Darkly, which follows a drug addict narcotics agent who starts to inform on himself without knowing it – about as paranoid a premise as you could imagine. Although Dick was self-aware enough to know that he was living out the cliché of a brain-fried Californian junkie. On his apartment wall was a poster with Joseph Heller’s famous phrase: “Just because you’re paranoid doesn’t mean they aren’t after you”.

In 1974, Dick had an epiphany which would define the final chapter of his life. A young woman came to his house to deliver painkillers. When Dick opened the door, light glinted off the locket around her neck, striking him with an “intelligent pink beam of light”, which he believed to have emanated from an extra-terrestrial deity he would come to call Valis.

He started believing that he was telepathically linked to a 1st century Christian called Thomas living in the Middle East and fleeing Roman persecution. Valis would beam him information in compressed waves every night. Over the next eight years he would try to make sense of these messages in an “exegesis” – 2.5 million words of rambling religious prose.

Dick didn’t live to see Ridley Scott’s masterpiece based on his 1969 novel, Do Androids Dream of Electric Sheep? He died of a stroke in 1982, three months before Blade Runner was released. But Dick had been shown some footage and understood the significance of the film. In a letter to the production company, five months before his death, he wrote: “The impact of Blade Runner is simply going to be overwhelming, both on the public and on creative people – and, I believe, on science fiction as a field.” Dick had seen the future, one last time.