Director James Marsh behind the scenes of the Stephen Hawking biopic “The Theory of Everything,” opening Friday. THE CANADIAN PRESS/HO Liam Daniel/Focus Features

TORONTO - When Stephen Hawking offered to lend his computerized voice to the new movie "The Theory of Everything" — which details his romance with first wife Jane — filmmakers saw it as "a gift."

Director James Marsh felt a "huge responsibility" to both Stephen and Jane Hawking in making the biopic, which opens across Canada in November. So he was anxious when the 72-year-old physicist saw the film for the first time.

"He gave us perhaps the best endorsement you could have by saying it's broadly true. And that's kind of what we hope for, to be broadly true in a biography where you have two hours to tell 25 years of someone's life," said Marsh in a recent interview at the Toronto International Film Festival.

"He then offered us his voice to use in the film. At that point, we weren't using his electronic voice, it was a different kind of voice that we had created... And that felt like an endorsement in the form of a gift, which is pretty nice too."

In "The Theory of Everything," Hawking's life story is told through the prism of his first marriage. Eddie Redmayne and Felicity Jones play the young lovers who are tested by Hawking's sudden diagnosis with ALS.

Marsh said that when he first read the script by Anthony McCarten, based on Jane Hawking's 2007 memoir "Travelling to Infinity: My Life with Stephen," he felt the "great discovery of it was that it was a love story."

"The love story gave a perspective on the career and the disability that felt very interesting," he said.

"The tension between these three trajectories — the course of the illness, which gets progressively more devastating, the course of the marriage, which gets progressively more complicated, and the scientific career, which gets progressively notable and public — felt like a fascinating engine to build a narrative around."

The film opens with Stephen and Jane's first meeting at Cambridge University in the early 1960s. Soon after, the aspiring cosmologist is diagnosed with the motor neuron disease and given two years to live. Though he sinks into a deep depression and tries to push Jane away, she stands by him and the pair marry and have three children.

But as Jane watches her husband undergo drastic physical changes and begin to require an overwhelming level of care, she looks for outside help — and finds it in Jonathan Hellyer Jones (Charlie Cox), a church choirmaster with whom she shares a powerful, hidden attraction.

"That felt like the heart of it," said Marsh. "The story of a third party coming into that marriage and that becoming complicated but also curiously sort of decent and respectful at the same time, that felt like really interesting dramatic territory to be in."

Redmayne has been praised by critics for his transformative performance, in which he embodies the scientist's physical deterioration as well as his witty, charismatic persona. Jones has also won accolades for her fierce portrayal of Jane.

Marsh, a documentary filmmaker who won an Academy Award in 2008 for "Man on Wire," said he hoped the audience would have sympathy for all the characters involved.

"It's actually tougher as a dramatist to try and take decent people doing the best they can do and the conflict they have. It's really interesting and more delicate to get at than a more broadly oppositional situation," he said.

"There's no villains here. There's no bad people. There's good people doing their best and sometimes hurting each other, with the best intentions."

"The Theory of Everything" opens Friday in Toronto before screening in other cities.

— Follow @ellekane on Twitter.

News from © The Canadian Press, 2014