Never underestimate the power of playing "a rather restrained man in a suit", Oscar winner Colin Firth said Tuesday as he presented a well-received biopic about a legendary American literary editor.

"Genius", which drew warm applause at the Berlin film festival, tells the story of Max Perkins, who worked with some of the 20th century's greatest authors including F. Scott Fitzgerald, Ernest Hemingway and Thomas Wolfe.

The picture stars British actors Firth and Jude Law playing the taciturn Perkins and the exuberant Wolfe, in a partnership that required the editor to harness and tame the writer's raw unvarnished talent.

Firth and Law said the script gave them a chance to generate sparks as two polar opposites whose collaboration made Wolfe one of the most admired novelists of his generation. Their joint creative output left the "genius" designation of the title up for grabs.

"One of the biggest challenges was in really celebrating and bringing to life the speed of thought with which these two great men converse," said Law, who adopts a broad Carolina accent for the role.

"The rhythm and the music that was to be found between these two men was very much a part of making their intellectual abilities clear. (There was a) staccato rat-tat-tat between us."

Firth in a mankini?

Firth, who won an Academy Award for his role as George VI in "The King's Speech", admitted that he was often the go-to actor for buttoned-up repressed types.

"It's not the first time I've played a rather restrained man in a suit," he said with a sly smile.

"I just get asked to play them. The suit is the costume, I put it on. If someone wants me to wear a mankini in a film, I am available. If anybody wants to free me from restraint... I am ready to burst out of a cake," he joked.

But he said that beneath the apparently still waters there were often rich depths to plumb as an actor.

"You'd be surprised how much variation I think I can find within the confines of a suit," he said.

"I find repression really interesting because I think there's an awful lot going on inside there. And I think mystery is fascinating in all art forms. The more we're left to guess at, the more that's left out, the more that's left unexpressed.

"Probably it is my fascination with that that led me to be such a consistent wearer of suits."

Rampant exhibitionism

Firth said that playing an editor meant being an unsung hero behind the scenes, a refreshingly old-fashioned concept in an age of hyper-exposure on social media.

"He was someone whose eye and ear were so finally tuned, his judgement and his integrity were so intact and yet he didn't want any credit whatsoever, his instinct was to remain invisible, particularly in an era where we are all clamouring to be visible," he said.

"There's a kind of rampant exhibitionism (now)."

Perkins cultivated strong personal relationships with his authors, who were often conflicted figures plagued by addictions, unhappy love affairs and writer's block.

Wolfe had a long and tumultuous liaison with an older married woman, theatre set designer Aline Bernstein, played by Nicole Kidman, who basks in his creativity but suffers when he periodically strays.

Perkins tries to coddle and cajole his writers including Fitzgerald (Guy Pearce) and Hemingway (Dominic West) toward greater output, serving as a stern father figure and an endlessly patient curator of his clients' best work.

"He was not a proofreader," Firth said.

"He wanted to preserve the integrity of books. Rather than an anal act of manual labour, just cleaning up text, it's a much more creative process."

"Genius", the debut feature by British theatre director Michael Grandage, is one of 18 films from around the world competing for the Golden Bear top prize at the Berlin film festival, to be awarded by a jury led by Meryl Streep on Saturday.