Benedict Cumberbatch had to "step out of his comfort zone" to play Doctor Strange.
The 40-year-old actor - who stars as the Marvel superhero in the hotly-anticipated movie - has teased the film will feature him doing "action hero stuff on a level" he never has before.
Speaking at the London premiere of Doctor Strange, he said:
"People ask me what I have in common with my character and I feel that's really it. I was having to do action hero stuff on a level I've never done before and wire work and kung-fu moves and casting these spells.
"Amazing movements like tutting with the fingers and all these delicate hand movements as well as body posturing. I was learning that as much as my character was, so both of us were stepping out of our comfort zone so that's something I could draw on for the characterisation."
Meanwhile, Benedict - who has 16-month-old son Christopher and is expecting a second child with his wife Sophie Hunter - previously opened up about the "psychologically and physically" demanding role.
He said: "He goes through so much psychologically and physically, which I can testify to as an actor. Kevin Feige went, 'I don't think we have put an actor through quite as much as this.' I said, 'I'll wear that badge with pride.'
"It was a tough shoot from that point of view. It was very, very physically demanding. Not just getting all hench, as they say in Wales, the buffness you need for the superhero stuff.
"But also just day-to-day fitness and the stamina to do 14-15 hour days with very little turnaround and very little sleep and a baby at home and all the rest of it.
So I did go through quite a lot. No pain, no gain. But for the character, hopefully it'll show."