The first thing Sixto Rodriguez asks me to do when I sit down to interview him in a film distributor's office in London is to tell him all about myself. He's eager to know everything: who I am, where I'm from. ("Is that an Irish accent? Erin go bragh!") The Observer's photographer is also required to give a potted history of himself before Rodriguez submits to having his photo taken. He looks the epitome of the veteran rock star – black suit, black-rimmed glasses, black hair down to his shoulders – but he couldn't be more self-effacing or more generous with his attention. As for his own life and career, the subject of a riveting new documentary called Searching for Sugar Man: "Oh," he says, "it's just a typical rags-to-riches story. Better that way than riches-to-rags."
Actually, it's a bit of both, and there's nothing typical about it. When Rodriguez first came to notice at the start of the 70s, he had the makings of a folk-rock star – the next Bob Dylan, as his co-producer Dennis Coffey put it. But somehow stardom eluded him. His albums, Cold Fact and Coming from Reality, sank without a trace in the US and Rodriguez sank with them. Bizarre rumours went about that he had died – of a heroin overdose or by setting fire to himself on stage. In fact, as he recalls now, he returned quietly to Detroit and became a labourer. "I did a lot of heavy-lifting – construction, demolition, that kind of thing. Dusty, dirty work." Meanwhile, totally unknown to him, his music was gaining a huge fanbase in South Africa where its politically charged lyrics had struck a chord with a growing anti-apartheid movement. His South African fans believed him dead, and neither word of his popularity in that isolated country nor royalties from hundreds of thousands of his albums sold trickled back to the US.
The documentary tells how, after the fall of apartheid, three dedicated fans finally tracked Rodriguez down to a tiny house in Detroit and flew him to South Africa in 1998 for a triumphant, back-from-the-dead tour. "It was incredible," he says. "They were just so good to me. And the stories I heard! One soldier said: 'We made love to your music, we made war to your music'. Another person had a tattoo of the Cold Fact cover." He shakes his head. "It was amazing."
He's played in many countries including the UK since then, but outside South Africa and Australia he remains a niche interest. Searching for Sugar Man, which won an audience award and a jury prize at Sundance earlier this year, is likely to change that. "We're getting bookings. We're going to LA after London, and we got a call to do Australia next spring."
Rodriguez turned 70 last week but this new success, four decades later than expected, doesn't seem to concern him. "I haven't reached the plateau yet," he assures me. "I feel fit and ready."