When, in 1949, New York-based poet and critic John Malcolm Brinnin becomes director of an arts centre in the city, the first thing he does is write a letter.

The recipient is a young Welsh poet. Brinnin admires him so much, he wants to invite him to America to read, lecture, make friends and influence people - and, perhaps, bask in a little reflected glory.

The invitation is duly accepted and, on February 21, 1950, Brinnin finds himself at New York's Idlewild airport awaiting a flight from London. Five years on, reflecting on the start of what would be a tumultuous friendship, Brinnin sets down in memoir form his first impressions of the man he went there to meet: "Bundled like an immigrant in a shapeless rough woolen parka, his hair as tangled as a nest from which the bird has flown, his eyes wide, scared, as if they sought the whole dreadful truth of America at once, he came into the zero cold of a frosty bright morning."

The visitor is Dylan Thomas, of course, the hard-living, hard-loving and even harder-drinking author of some of the most luminous verse of the 20th century.

Now Brinnin's memoir of his time playing cheerleader for and nursemaid to the notorious poet on his four trips to the US has been turned into a film, Set Fire To The Stars, to be released next month. Thomas is played by Anglesey-born actor Celyn Jones, the film is directed by Welshman Andy Goddard and the soundtrack is by Gruff Rhys of Super Furry Animals. But the pivotal role of Brinnin is taken by a Hollywood star who had never been to Thomas's birthplace of Swansea before he undertook a gruelling 18-day shoot there early this year, and who even now is probably more familiar with Middle Earth than Mid Wales - Elijah Wood, who played Frodo Baggins in Peter Jackson's epic adaptation of JRR Tolkien's The Lord Of The Rings trilogy, and returned to the role in 2012 for the first part of Jackson's take on The Hobbit.

"I was sent the script and fell in love with it immediately," the 33-year-old tells me as he sips an espresso in an Edinburgh hotel suite. "It was brimming with energy and life and movement, and I loved the characters and the relationship between the two of them. I knew who Dylan Thomas was and certainly that he was a significant literary figure - but I didn't know his work, so it was really my introduction to him."

America's own introduction to Thomas wasn't quite as gentle. Nor, for the bluebloods of the New York literary circuit, was it as fondly recalled. Put simply, the Welshman raised hell, and in Set Fire To The Stars we watch as he careers drunkenly between low-life pubs and high-class literary parties, scandalising guests at the second and delighting the denizens of the first.

There are memorable supporting roles from Kevin Eldon and Fife-born Shirley Henderson, and Kelly Reilly appears as Caitlin Thomas in a hallucinatory sequence set in a forest. But for the most part, the richly cinematic black and white film is an intense two-hander between the Welsh actor and his diminutive American counterpart.

Mind you, there's little in Elijah Wood's career to date which has been predictable, so why not travel to Swansea to shoot a black and white film that's set in New York and has virtually no cast? After all, this is the actor who founded his own record label in 2005, programmes a horror movie festival in Los Angeles in his spare time, once featured in a film about West Ham football hooligans and currently stars in the US TV remake of deeply odd Australian comedy Wilfred. In it, Wood plays a depressed thirtysomething who sees his attractive female neighbour's pet pooch as a man in a dog suit. Nobody else does, which leads to a very unlikely friendship and a difficult three-way relationship. It was adapted for cable channel FX by Family Guy showrunner David Zuckerman, which immediately places it at the edgier end of the TV spectrum. So, post-Rings, is that where Wood likes to be?

"I think I'm always looking for something new and I'm always looking to challenge myself," he admits. "You don't move forward unless you take risks, either as an actor or as a person. Otherwise it's just comfort zone. So if Wilfred is representative of that, it's great. It's certainly something that's a core belief of mine. And to a certain degree, perhaps that's why I was attracted to this as well because I hadn't done anything like it in a while and it was out of my comfort zone. That's a deciding factor sometimes."

Born in Cedar Rapids, Iowa in 1981 but resident in Los Angeles for many years, Wood's first break came aged just seven when he worked with Gone Girl director David Fincher - on a Paula Abdul pop video. Other big names and big-name films he worked with or appeared in, however tangentially or briefly, include Back To The Future II, Richard Gere vehicle Internal Affairs (playing Billy Baldwin's son), Ang Lee's The Ice Storm (as Sigourney Weaver's son) and Barry Levinson's Oscar-nominated Avalon.

Then, in 2001, came the big one: Peter Jackson cast him in the lead role in The Lord Of The Rings. Soon, his elfin good looks and piercing blue eyes were staring out from billboards and magazine covers all over the world as he starred in a movie that had long been thought unfilmable. It also gave him his first taste of a mega-budget studio film. Well, sort of, he says.

"The funny thing about Lord Of The Rings is that as big as those films were they always felt like independent films. Partly because they were shot in New Zealand, partly because everybody who was involved was embarking on something they'd never done before. Going back on The Hobbit, the machine is much bigger and the budget's larger, but the feeling is still quite similar."

In a word, he says, it still feels "homemade".

What's unarguable, however, is that his role in The Lord Of The Rings saw him become part of an ensemble cast which still reads like a who's who of 21st-century acting talent. So which of his co-stars did he find the most inspirational? "Aw man," he says, looking into his now empty cup for the appropriate response. "There have been some incredible people. Ian McKellen comes to mind. He's wonderful and generous and kind - a total sweetheart, and a brilliant actor who works really hard. And I found Viggo [Mortensen] to be inspiring, especially as a lead-by-example kind of actor. He gives 110%. There was a scene in The Lord Of The Rings where he got hit in the face and knocked half his tooth out. They were going to send him to the doctor - but he just asked for superglue!"

Youthful-looking, polite, thoughtful and approachable he may be, but Elijah Wood is still a Tinseltown veteran with a quarter of a century of experience behind him. He may view Lord Of The Rings as somehow insulated from the worst aspects of the studio system, but it's hard to believe the cynicism that exists elsewhere in the film industry hasn't affected him somehow.

"Well, I hate cynicism," he counters. "I'm naturally enthusiastic and I haven't lost my enthusiasm. I think part of that is because I keep going towards the thing that makes me happy. I work on the projects that I find fulfilling, keeping a mind on my integrity. So I feel I've kept my path pure in that sense ... I've rarely had shitty experiences in acting and within the industry."

But, he adds, "I see the industry for what it is. Right now it seems to be about risk management, certainly at studio level. They're investing a lot into things that have pre-existing fanbases so as to mitigate their loss. So there are remakes, franchises, and sequels."

And, as a result, far fewer dreamlike black and white films about a poet and his gentle minder in 1950s New York, which is a pity. Still, as Wood himself says: "You can look at the larger landscape and say it's really disappointing. But then you avert your eyes from the studio system and it's extremely rich and exciting ... Every year I see films from foreign countries and from American independents where people with incredible voices are doing incredibly interesting things."

Dylan Thomas didn't need much excuse to raise a glass - but that sounds like a sentiment he'd consider worth a toast.

Set Fire To The Stars is released on November 7