Aaron Eckhart’s latest role is very clearly a physically-demanding one. He portrays Frankenstein’s monster in a thriller by the creators of Underworld, and it doesn’t take looking at the trailer to understand that in this world where gargoyles fight demons, there is going to be a lot of action.

Plus, after all, the soulless creature wanders the Earth alone for two hundred years, so he has got to be pretty savvy fighting, and definitely strong all around.

So Eckhart is tough and chiseled on the exterior – but it wasn’t just a taxing role on the surface.

“This was probably the hardest movie I ever made. It absolutely depleted me, both emotionally and physically,” says the 45-year-old actor during a roundtable interview while promoting I, Frankenstein in Toronto. “[I was] dwelling on the story and just always portraying this feeling of rejection and loneliness. [Writer and director] Stuart [Beattie], when we were talking about the movie, always said that he wanted to see me filled with rage. ‘I want to see rage. I want to see you pissed.’”

So it is with anger and purpose that Eckhart carries himself in this role as the damned creation, given the name Adam. After being forged and seeking meaning, Eckhart’s creature feels betrayed by his creator and wanders the world alone for centuries, until being cast in an ancient war between heaven and hell.

There are plenty of special effects and exciting set-pieces, but Eckhart explains just to what extent he wanted to feel the pain that Adam would have felt.

“There’s just this deep sense of misunderstanding and this hatred that he has for his father. He has such a wanton desire for love in the book that goes unfulfilled, and over time this hatred just gets built up and built up,” he says. “His father never gives him an explanation. He tells him he wishes his son was dead.”

To prepare, Eckhart informs that he went online to understand the plight of those children who have been abandoned, neglected, and abused. “I looked at videos of abused children telling their stories. Stories about psychologically, physically, and sexually violated children. And if you guys ever want to understand that kind of rage or see what that kind of rage is like, you should look at that sometime.” He speaks on one video in particular that he viewed over and over, one that shows a young girl confronting her father who had constantly assaulted her.

Eckhart, who can dabble about cigars and crack jokes in the same breath as dishing on something far more serious, lowers and slows his voice while reflecting on such intense preparation. He pauses throughout while explaining, and at one point admits he might cry just recalling the experience.

He carries that rage with him through the film; it manifests as distrust, as carelessness, for his headstrong Adam cares not for the human race or the fate of souls.

“There are millions of kids out there that might feel the same way that aren’t able to express it like this young woman was, and how that can ultimately affect your entire life and your future relationships,” he continues. “ It’s crazy to try to think about it all the time, but I tried to stay in that area the entire movie, and that’s what was really draining.”

His insight certainly adds an interesting layer to a film that is on paper a January action thriller based on famed source material. Eckhart worked out tirelessly for the role, and was definitely excited to take on such a tough-guy role after being teased for playing a weak-willed President alongside Gerard Butler’s hero in last year’s Olympus Has Fallen.

Eckhart, who has deliberately picked certain roles and avoided others over his career, was lauded for his performance in Thank You For Smoking and found himself in a key role in the blockbuster The Dark Knight as Harvey Dent. He now gets a turn as a physically-impressive hero, doing nearly all of his own stunts, and embracing the change of pace.

“I just got to a point where I would get scripts and it would just be page after page after page or monologue after monologue, and I just would sigh and think, ‘I just don’t want to say any more words, I’m sick of it! Why am I saying so much? I have nothing to say! What else could I say?”

So there are lighter moments, and while the conversation turns surprisingly somber and grave when he spoke about his mental preparation, he also gave a hint to his morbidly comic side when the entire interview started, explaining why now for such a film.

“Well, I am going to be dead soon, so I wanted to be able to do at least one action movie before I die.”

I, Frankenstein opens Friday, January 24.