Ioan Gruffudd said James Cameron was like a "man possessed' while filming 'Titanic'.
The 43-year-old actor - who starred in the award-winning movie as officer Harold Lowe - admitted the atmosphere on the set of the 1997 blockbuster was always "tense" because the director was under a lot of pressure from two studios to finish the movie.
Speaking to the Daily Telegraph newspaper, the actor said: "If James Cameron was here now, he'd be delightful. But oh, my goodness, on 'Titanic', he was a man on a mission.
"There were two studios breathing down his neck... he was a man possessed so the atmosphere was so tense, but he was just getting this movie done."
Gruffudd also starred in the 2005 Hollywood superhero movie 'Fantastic Four' and the subsequent sequel 'Fantastic Four: Rise of the Silver Surfer' as Mr. Fantastic but found making a superhero film isn't the most "satisfying experience" because there's so much CGI involved.
He said: "Making those movies isn't the most satisfying experiences, it's all green screen and technical stuff but once it's put together it's extraordinary, doing the promotion, travelling the world first class.
"It was just brilliant for a chap who grew up in Aberdare."
Now the actor is older he believes he gets considered for more roles because he doesn't look like a "leading man" anymore.
He said: "It's exciting because there are all sorts of parts I'd never have been considered for in the past because I was too young and looked too much like a leading man.
"Now, I've got a bit of weathering. I've put on a bit more weight, I'm a bit more jowly. I can play a character a real person."
Gruffudd's name was also thrown into the mix about who could replace Daniel Craig as the next James Bond but the actor has confirmed he was never approached for the iconic role.
He said: "I defy any British actor to deny they've not stood in front of the mirror and said 'Bond, James Bond'."