Tom Hiddleston had to play down his "irritating optimism" to get into his latest role of a "melancholy" vampire.
The Thor star plays Adam, alongside Tilda Swinton's Eve, in Only Lovers Left Alive, and playing the reclusive musician was a "big stretch" for him, he said.
Speaking about his character at an event at the British Film Institute on London's South Bank looking ahead to the Toronto and Venice film festivals, he said: "He is romantic, and melancholy, and poetic, and sensitive, deeply creative, and nostalgic for a pre-digital age where creativity was more of an endeavour...and he's a vampire."
Hiddleston described working with Swinton as "amazing", adding: "She's an extraordinary, extraordinary artist. It really felt like a dance in a strange way because Adam and Eve became alive as much as we invested in them."
A tale about the relationship between the two vampires, the London-born actor said Swinton's character in the film complemented Adam.
"In a way her breadth can hold Adam's complexity, and it's really a love story between these two fine and delicate creatures of the night," he said.
Hiddleston said he could see similarities between himself and Adam, but added that he is a much more optimistic and happy person.
"There's a lot of me in Adam for sure, but Adam is also darker than I am," he said.
Adding: "John Hurt is in the film and Adam is described by his character as a 'suicidally romantic scoundrel'.
"I have probably an irritating optimism sometimes in myself and I had to turn the volume on that down."
Taking on the role did not intimidate him and he said he enjoyed challenging himself.
"It was wonderful, because acting is the privilege of living in the shoes of someone else for a time, and Adam was a big stretch for me," he said.
Hiddleston, who starred in Midnight in Paris, had to lose weight for the part, but said he does not believe a performance should be judged on how much an actor has changed their appearance.
"I had to change my physicality to some degree.
"I'm very sceptical of this current vogue of performances being judged according to how much weight you put on or lose, because I don't think it's what it's about, truly.
"I just had to do more exercise and eat a bit less," he said.
The actor is taking on Shakespeare in December when he will play Coriolanus at the Donmar Warehouse - and he has started learning his lines already.
"It's a monumental learn. It's one of the longest parts.
"I've started already so Coriolanus is occupying every last brain cell that I have. It's wonderful though," he said.