Three months of exhaustive research helped Kutcher get inside the head of a man he never met. Or it could be that Jobs got inside his.

At a recent screening in San Francisco, Kutcher passionately defended Jobs' controversial decision not to give stock options to some of the earliest Apple employees who had not lived up to his expectations.

"I think Steve was extraordinarily loyal to people he felt were loyal to him," said Kutcher, who called Jobs this generation's Leonardo da Vinci.

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Though the film received tepid reviews after premiering at the Sundance Film Festival in January and has been criticized for giving too much credit to Jobs for Steve Wozniak's vision for the personal computer, Kutcher has been praised for moments in which he seemed to embody Jobs — staring himself down in the mirror after denying paternity of his child or standing triumphantly on the floor of the West Coast Computer Faire with Wozniak to unveil the Apple II.

Even when he's showing Jobs at his most callous, Kutcher humanizes the man who died from complications of pancreatic cancer in 2011.

"There were these inconsistencies in his behavior," Kutcher said. "I wanted to figure out why he made these choices. Why this brilliant man did not seek medical treatment for something he knew would be fatal. Why this guy who was so brilliant would use such brute verbal force to make changes."

He immersed himself in Jobs' spiritual beliefs with Paramahansa Yogananda's "Autobiography of a Yogi" and Ram Dass' "Be Here Now" and in his musical influences by listening to Bob Dylan and Joan Baez. He studied Thomas Edison and Ansel Adams.

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For scenes set in the garage of Jobs' childhood home in Los Altos, Kutcher read up on integrated circuit design. When driving in his car and as he fell asleep at night, Kutcher played some 100 hours of every Jobs interview and speech he could find.

That attention to detail extended to Kutcher's physical appearance in the film. Skeletally thin, the actor landed in the hospital for two days after losing 20 pounds on the fruitarian diet Jobs followed.

But Kutcher gained the most insight into Jobs by meeting some of the people who knew him best.

"I got to meet Avie Tevanian," Kutcher said with a tone of awe about the former Apple software wizard. "That's sick."

Kutcher also met computing pioneer Alan Kay of Xerox PARC fame.

"I gave Ashton a picture of the real Steve from the point of view of someone who knew him for many years, who talked with him every few months on the phone," Kay said. "Steve was not an idol or a myth or a god."

Kutcher said Kay recalled the anguish Jobs felt over sharp criticism of the Macintosh.

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"Alan said to him, 'Steve, the only reason they are criticizing the Macintosh is that you built a personal computer that is good enough for people to criticize,'" Kutcher said. "Since Steve was adopted, he felt like he was rejected by his birth parents. He filled that hole by building beautiful things people would appreciate. When they rejected the products, they were rejecting him."

Gad, who plays Wozniak, said he'll never forget the first time he talked with Kutcher over Skype and encountered his encyclopedic Jobs knowledge.

"He knew everything not only about Jobs but could literally rattle off the tiniest detail about Steve Wozniak as well," Gad said. "I hung up with him and ordered every piece of literature and watched every single video I could like a student who has to cram for the SATs the night before the exam."