Ten years ago, an audience with Christopher Lloyd was as hard to score as plutonium. He didn't do print, he didn't do radio, and, unless pressed, he steered clear of chat shows. An appearance on Wogan in 1991 went down in the annals of difficult TV: Lloyd was perfectly courteous, but so bashful as to be near mute.

"I was just very shy," he says. "I was never anxious to do talk shows as I didn't know what to say. And I don't feel I have any inherent interest." He speaks thoughtfully; his voice generous, humorous, kind. "But as I'm getting older I feel I want to be able to share whatever I know, if it means something to someone."

And it's only recently the legacy of his best-known work has really become apparent. This year marks the 25th anniversary of the first of the three Back to the Future films, in which he played the wild-eyed inventor Doc Brown. Photos of fan events and crew reunions show him gamely grinning away, looking aptly ageless – he's still only 71.

"I've met people who say those films changed their lives. I'm so proud to have been part of a creative enterprise that had such an effect."

In last year's Call of the Wild 3D, Lloyd played another life-affirming mentor: a recently bereaved Montana old timer whose granddaughter comes to stay and gets rehabilitated from her city hang-ups by granddad's care, an affectionate wolf and a spot of sled-racing. It's a sweet, old-fashioned film, but hardly a stretch – Lloyd has been a Broadway staple for 40 years, and is prepping for a Death of a Salesman revival. He's one of the most recognisable, memorable American character actors of the late 20th century. But for the past decade he's made almost nothing but low-profile family films. Why?

"Well, I don't really plan it," he says. "The jobs come and I take a look at them. I liked this one particularly because I've played a lot of characters that are way out there. Grandpa Bill isn't wacky, he's just a decent, well-grounded man."

It's an answer that shows how much more akin to this chap Lloyd is than he was the scene-stealing likes of Doc or Fester Addams or Judge Doom. He's a man of mellowness, not ego – far from bitter at the lack of meaty roles, just gently getting on with what he's offered. In 2008 his house in rural California fell victim to the forest fires. A TV news crew raced to the scene. Lloyd wasn't raging; he was soft-spoken, full of humility.

Until recently he also had a place in Montana. He, too, hears the call of the wild. "There's something overwhelming about being in raw nature. It's got an aura about it is that is really kind of majestic and spiritual. It's good medicine."

These days, Lloyd likes hiking and fly-fishing. Between jobs in the 70s, he bicycled through Italy with a friend, then got the ferry to Greece and clopped round for six months by horse and cart. He once cycled solo up the coast from San Diego to Seattle; another time from the west coast to Nova Scotia. He likes, he says, to go it alone, despite having four long marriages behind him. "When travelling I like not being tied to someone else's rhythms. I'm somewhat of a solitary person."

In London a few years ago on a break from a shoot, he hired a barge to journey up the Thames. "I don't remember exactly where I went, but it was just beautiful popping along at about five or six knots."

So he's not really into speed? "It doesn't sound like that, does it?" he says, laughing. "I got a few speeding tickets when I was young, but I'm a little more like the turtle than the hare."

Lloyd is that rare thing: an iconic actor who's no showboat. It's easy to picture him on that barge, gliding peaceably along, unhurriedly in search of lost time.

Call of the Wild is out now on DVD from Icon Home Entertainment