Securing an interview with James Cameron, Hollywood's mightiest, most terrifying director, is not dissimilar to the plot of The Wizard of Oz. First comes a scene-setting, pre-meeting with "his people", to talk about the meeting. Then, a thrilling flight (at dawn) to Belfast, where the Avatar and Titanic director is launching the latter in Blu-ray 3D. After that I must run the gauntlet of ferocious creatures - not lions and tigers and bears (Oh My!), but menacing publicists and hatchet-faced apparatchiks with clipboards and schedules.
I am whisked off to visit "The Titanic Experience" - a breathtaking visitor attraction, all the more so when undertaken at a brisk guided trot that gives me a stitch. Next, I am obliged to stay up well past my bedtime to watch the spectacularly vivid Titanic in 3D. Least, but not last, I must be in the hotel lobby at 7.25 the next morning for an unspeakably early press conference.
When I don't appear (not unreasonably, given that my appointed slot with Cameron isn't until 4.20pm), the Wicked Witch of the Production Company e-mails me in my room. Then she texts me. Before ringing me. I am told that Scarecrow, Tin Man and Lion are already on the coach and I must follow the Yellow Brick Road behind them, in a taxi. I dutifully agree, but instead go back to sleep in my field of poppies, trusting my ruby slippers to carry me through. It's a big ask, even for magical footwear.
Cameron, who also made Aliens and Terminator and The Abyss, is an undisputed big beast of the blockbuster jungle with a volcanic temperament to match. Tales of his temper are legion. His infamous motto "I eat stress for breakfast" fails to mention that he rips the wings off actresses for lunch; post-Titanic, Kate Winslet swore she would never work with him again after she nearly drowned, came down with flu and chipped a bone in her elbow. He also tears strips off his technical team, has been known to hit actors with a stick to provoke the perfect on-screen response, and, legend has it, he once took a runner's mobile phone and nail-gunned it to a wall.
When I finally gain my audience with movie making's equivalent of the Great and Powerful Oz, I am poised for fight or flight, guessing that flight would be wisest. And what do you know, he turns out to be Professor Marvel instead: a wellspring of expertise on undersea exploration, Nasa technology and ecological living, and, if not exactly avuncular, then certainly not as scary as those tiptoeing about him would have us Dorothys believe.
"That's the beauty of my reputation," he says, drily. "I don't have to shout any more, because the word is out there already. I did once nail-gun 20 mobile phones to a wall on the Jay Leno Show, but I swear it was the first time I'd ever done it."
Canadian-born Cameron, 58, cuts an imposing figure. He is tall and rangy and oddly ageless, with a shock of white hair, a matching goatee and extraordinary long, bony fingers. Much more extraordinary is the way he doesn't bite my head off, either literally or metaphorically, when I take a deep breath, clutch my imaginary Toto to my breast and demand to know why in Zsa Zsa Gabor's name he has been married five times.
"What can I say, I can't resist an upgrade," he says, with a smile. "Believe me, I think you'll find that I was the low-maintenance one in most of my relationships, I just kept picking complex, independent women.
"Look, I'm a perfectionist and I strive for excellence, and if that means more than one take, then I'll keep plugging away. As I told my wife Suzy on our wedding day, this is my final take." Perhaps you have to be in the movie business to find that as romantic as Cameron does, but he is clearly a lot mellower than the mythology that surrounds him.
"Well," I find myself saying aloud. "You aren't at all what I expected. But then I haven't spent as much quality time with you in a 3 feet-deep recreation of the Atlantic as Kate Winslet has."
With a note of steel in his delivery, he replies: "Kate shouldn't have said what she did. But she felt she needed distance after filming, and there was no ill will when she came in a few months later for re-shoots. And certainly no bad feelings when she was nominated for an Oscar."
Quite so. Titanic was nominated for a staggering 14 Academy Awards, and took nine of them. The three for Best Picture, Best Director and Best Film Editing went to Cameron. I wonder whether he keeps them in his downstairs loo, like Brits do.
"What, you mean in the rest room?" he asks, looking bemused. He keeps them, as befits a man free of false modesty, on his drinks table. "I wonder what Meryl Streep does with hers - she's probably had to build an extra wing on her house."
Cameron's home on a Californian ranch is relatively unshowy, though he's also bought a pricey farm in New Zealand. Both properties have extensive organic kitchen gardens, but just one television each. This may only be used to watch films, and strictly en famille.
He drives a Toyota Hybrid that is a whole six years old - the Los Angeles equivalent of Del Boy's Reliant Regal - and recently became vegan, along with his family of five children, aged from five to 23. Do his children really share his vision of self-sufficiency and salad?
"No, of course not, the kids want hamburgers and Coke because they're kids," he says, almost snapping. "But all of human consciousness is five years old emotionally. It's not a requirement to eat animals, we just choose to do it, so it becomes a moral choice and one that is having a huge impact on the planet, using up resources and destroying the biosphere."
Cameron's idea of downtime is always biosphere-friendly, usually "kayaking or scuba-diving" with his children; nobody gets to sit around gazing at screens, which is ironic given that his estimated $700 million fortune rests on the willingness of cinema audiences to do just that.
His wife, to whom he has been married for 15 years (the others never made it past their paper anniversaries), runs a progressive school, with great emphasis on outdoor living and the virtues of simplicity, hard work and personal responsibility.
"Luxury for luxury's sake and expense for expense's sake disgust me," he says, which is weird coming from a man who spent $300 million making his 3D sci-fi eco-extravaganza Avatar, which he also wrote. Having said that, it did become the highest-grossing film ever made, which might explain why 20th Century Fox has signed him up for Avatar 2 and 3.
Meanwhile Cameron, whose gimlet attention to detail is such that when he was working on Titanic 3D, he digitally rearranged the stars to match the night sky on the actual night the ship sank, has ploughed a "big chunk of money" into the Avatar Foundation, an NGO that supports indigenous rights, environmental issues and lobbies against global warming.
His own connection to the natural world resides mainly in his passion for undersea exploration. He has visited the Titanic wreck 33 times, made 39 dives elsewhere and earlier this year became the first person to make a solo voyage to the floor of the seven-mile deep Mariana Trench, the very bottom of Earth's oceans and more than a mile deeper than Mount Everest is tall.
He organised and funded the trip himself and expects it to be one of many. And as in all the best movies (say, The Wizard of Oz), his journey to a faraway world taught him much about himself.
"It was when I first started doing expeditions that I learnt a lot about motivation and leadership," he says, which is his way of admitting that you can't scream and rant in a submersible and expect to come back in once piece.
"When you yell you do get results, and although that sort of hard-ass behaviour is rewarded in the film business, it's not the best way of managing people long-term. I'm still capable of losing my temper but I think I have it well under control and have had for quite some time."
As he'll be working with the same Avatar team for years to come, achieving excellence, day in day out, that will come as a relief to his crew.
"There were times in Avatar when things would go horribly pear-shaped, when the system crashed and burned and everybody looked crestfallen," he says, with fond nostalgia. "And you know what I would do?"
Let me guess: spray the room with semi-automatic machine gunfire?
"No, I would stop everything and sit round a table and say: 'This is the good part, the decisions we make today will affect how this is done for the next 100 years. Yes, it's vexing, but we are pioneers.'"
And as Dorothy discovers when she returns to Kansas, being a pioneer is never easy.
'Titanic All New Collector's Edition' is out now on Blu-ray & Blu-ray 3D, from Twentieth Century Fox Home Entertainment; discoverireland.com