I meet Aaron Eckhart in London, early on a Saturday evening. He is dressed in a dinner jacket and a straight black satin tie for a secret assignation with Bafta. "I had it pressed for this," he jokes.
The suit is slim but not skinny, an important distinction for Eckhart, who, though so chiselled he could probably be used as a weapon, describes himself as "just an older man", determined to "take the sexuality out of it". (He is 48.) "Which is interesting in this business," he adds, "because they try to sexualise everything. You know, all the suits are rail-thin and they're tight and I'm like: 'You guys! What are we trying to accomplish?'"
If you think that's oversharing, it's nothing. Within five minutes, Eckhart has told me that for his new film, Bleed for This, in which he plays the washed-up boxing coach Kevin Rooney, he put on 18kg, bought huge trousers but never buttoned them up, and shot the whole film "with poison oak all over my backside". "Why are we talking about this?" he says, as if to himself.
Then he goes on.
"Three months before this movie started, I circled the day on the calendar and said: 'I'm gonna put away the arugula salad and I'm gonna go for pizzas and banana splits'." The weight gain led to a great deal of discomfort, he confides.
People who've seen Bleed for This all seem to emerge from the cinema with the same question: how long did it take you to realise Kevin Rooney was Eckhart? We first see him slumped on a floor in a stupor, and when roused, he moves so lethargically, and slouches so heavily over his enormous stomach that it's impossible to tell who the actor is. Even after he finally lifts his bald head it's not clear. Rooney is so far from the sort of alpha male role Eckhart seems cut out for that even if you know he's in the film, you assume he must be playing another part.
Ben Younger, the director, gave an early screening to Steven Soderbergh, who directed Eckhart in Erin Brockovich, and, Eckhart tells me, "Ten minutes after I had entered the film Steven said: 'Who is that guy?'"
The film, which might appear to be about Miles Teller's character, the boxer Vinny Pazienza, is at its best when it's about the relationship between the two of them. Rooney, who in real life had just been fired by Mike Tyson, went into decline. Pazienza hired him to orchestrate his comeback, but the idea had been cooked up by promoters who thought this was a simple way of putting both men out to pasture.
In Bleed for This, Rooney trains and nurses Pazienza, not as the tough guy of sporting lore, but as a canny outsider who favours honesty and kindness to oneself. Eckhart makes him seem almost maternal.
Rooney is one of two roles putting Eckhart back in cinemas - the other is as co-pilot to Tom Hanks in Sully, a film about Chesley Sullenberger, the pilot who safely landed a defective plane on the Hudson River. He is strikingly good in both movies.
So why isn't Eckhart more famous? Looking back at his performances over the past 20 years - as Chad, the sick joker, in In the Company of Men, as Julia Roberts' biker boyfriend in Erin Brockovich, as the slick tobacco lobbyist in Thank You for Smoking, as the disfigured district attorney who backs Batman in The Dark Knight - it seems more and more puzzling that he should have received relatively little praise.
Granted, Eckhart's hit rate hasn't been high - those great roles are just a few of 40 - and he has been markedly unconvincing in anything romantic, but he is persuasive in so many other ways: dark, nasty, hopeless, kind, charismatic.
"I've had an interesting career," he says.
"Look, there's things that I would like to erase, for sure."
He won't say what, and makes a gesture that suggests his work has gone in waves. But I think there's another element to it. It's just a hunch, but I start to wonder if he has a reputation for being tricky. His "it's not about me" message to other actors has the flavour of a note to his former self. There's something in the way Eckhart talks that reminds me more of sportsmen than actors. It's all about winning. "I'm a loner," he says. "I don't affiliate myself with groups."
"Does that make you easier to work with, or more difficult?" I ask.
"Oh, I think more difficult, definitely. Because, you know, I have other issues - besides loner-ism - that make me difficult."
Later, he says how annoying it is that actors are expected to be popular with film crews, as if it were some sort of "badge of honour", though they often have to generate a troubled state of mind when the cameras are rolling.
"If I were a director, I would say, 'Listen guys. This is what's going to happen today. If he's irritable, or if she doesn't talk to you, give 'em some space.'"
What's he saying about himself here? Eventually, Eckhart lets out a deep sigh and says, as if admitting defeat: "Ach! I have a terrible reputation. I'm just too intense for people."
Eckhart now thinks that he would have been more successful if he'd been more sociable. A while ago, he had what he describes as a "light bulb moment" at the Golden Globe Awards. He looked around him - at Steven Spielberg and Johnny Depp and all these Hollywood people he knew - and he said: "Aaron, you idiot. This is your family. Don't fight your family. Appreciate these people - love them."
"As opposed to doing what," I ask.
"As opposed to being competitive with them. As opposed to picking them apart, or saying 'Why you?'"
Describing the kind of films he would like to direct one day, he says, "I want to make hardcore relationship movies. About men and women telling each other the truth. I want raw, raw, raw truth on film."
When I suggest that sounds scary, he says, "It's so scary that nobody makes them."
• Bleed for This will be in New Zealand cinemas next year.