It took the Doors’ drummer, John Densmore, three years to visit the grave of his bandmate Jim Morrison after he was found dead in a Paris bathtub in 1971. He didn’t even go to the funeral. “Did I hate Jim?” Densmore pauses, although he is not obviously alarmed by the question. “No. I hated his self-destruction … He was a kamikaze who went out at 27 – what can I say?”

Quite a lot, it transpires. Morrison was a man who was spectacularly good at being a rock star – a lithe figure in leather trousers, prophesying about death, sex and magic on some of the biggest hits of the 1960s – Light My Fire, Break on Through and Hello, I Love You. But he was catastrophically bad at the rest of life. Like many alcoholics, he could be reckless, selfish and mercurial. “The Dionysian madman,” Densmore has called him – a “psychopath”, a “lunatic” and “the voice that struck terror in me”. He had lobbied to get Morrison off the road before his death, and even quit the band at one point. “Some people wanted to keep shovelling coal in the engine and I was like: ‘Wait a minute. So what if we have one less album? Maybe he’ll live?’” Why did he carry on? “Because I wasn’t mature enough to say that at the time. I wasn’t trying to enable him. It was another era. I used to answer the question: ‘If Jim was around today, would he be clean and sober?’ with a ‘no’. Kamikaze drunk. Now I’ve changed my mind. Of course he would be sober. Why wouldn’t he be? He was smart.”

Densmore, 75, is a defiant survivor of the music scene he helped build. This, perhaps, is why, in the decades since Morrison’s death, he has become not only one of the great chroniclers of the Doors, but the fiercest protector of Morrison’s legacy. To anyone who has read Densmore’s 1990 memoir – a book he says was “written in blood” – this may come as a surprise; later the book would form the basis for Oliver Stone’s (dreadful) Doors biopic. “It took me years to forgive Jim,” Densmore says. “And now I miss him so much for his artistry.”

Next month, a documentary about another of his bandmates, the keyboardist Ray Manzarek, who died in 2013, will be released. Manzarek’s relationship with Densmore was not smooth either. From the early 2000s, they were embroiled in a vicious six-year legal battle in which Densmore tried to stop Manzarek and the band’s guitarist, Robby Krieger, from touring under the Doors name as well as selling the band’s music for use on a Cadillac commercial. “I know. I sued my bandmates – am I CRAZY?!” he yells. People certainly thought he was. It is not usual to spend years in court trying to stop yourself from earning millions of dollars to prove a point about the value of artistic integrity over the pursuit of money. “What can I say? Jim’s ghost is behind me all the time,” Densmore says. “My knees were shaking pretty strong when they upped the offer of $5m (£3.8m) to $15m. But my head was saying: Break on Through for a gas-guzzling SUV? No!”

Manzarek and Krieger’s lawyers tried to paint Densmore as a dangerous communist – even citing a piece he wrote that was published in the Guardian as evidence for this – but eventually, and spectacularly, he won. He wrote a book about the case, published in 2013, and donated the profits to the Occupy movement. “Money is like fertiliser,” he says. “When spread around, things grow; when it’s hoarded, it stinks.”

Densmore is fluent in the language of the 60s elder: on the one hand, he talks of peace rainbows and pots of gold filled with love, despairing at the rise of “separatists and populists and borderline racists” running the US. On the other, he displays an almost chilling pragmatism about life and death, not uncommon among musicians of his generation, who lost so many friends to the era’s excesses.

“I interviewed Tom Petty a few months before he died,” he says quietly when I bring this up. The pair became friends during the court case – Petty’s song Money Becomes King, about a singer he once idolised who was selling his songs for a light beer advert, struck home with Densmore. “He had trouble with his hip. I guess he was taking painkillers and brown powder, too. Damn it …” he breathes deeply. “I just ache losing him.” He pauses. “Maybe it’s more noble to die in a friggin’ hospital with a bunch of tubes up your arm. I mean, it sounds horrible, but at least you rode the train all the way to the end – you never checked out early.”