Watch: David Harbour lifts the lid on his Violent Night training regime
When you think about the jolly figure of Santa Claus, it's probably fair to say that jiu-jitsu isn't something that comes to mind straight away. What about Greco-Roman wrestling?
The Stranger Things actor told Yahoo UK he didn't get the chance to speak to a Santa Claus trainer ahead of playing the role, because he was too busy getting his body ready.
Read more: Most unusual movie versions of Santa Claus
"My training was very different. My training for Santa Claus was jiu-jitsu and Greco-Roman wrestling. But that would have been very interesting to talk to a [Santa Claus trainer]," he said.
In the film, Santa is visiting the wealthy Lightstone clan on Christmas Eve when a band of money-hungry mercenaries hold the family hostage, triggering Mr Claus's long-dormant warrior side.
Harbour added that, although his training was mainly geared around how to convincingly hit bad guys with a sledgehammer, he did 'a lot of research' into the different versions of Santa Claus all over the world.
He said: "There's Saint Nicholas in the Christian tradition, who was the patron saint of repentant sinners, which I thought was really interesting. He wound up giving little gifts to children.
"There's the Weihnachtsmann in Germany. There's all of these different iterations of him culturally throughout the world and I thought that was really interesting."
Harbour said that Violent Night crafts an origin story for Santa Claus, which uses elements of folklore but also invents some lurid aspects of his past as 'a very different guy' thousands of years ago.
The film introduces Santa as a shell of himself, pondering retirement as he drowns his Christmas Eve sorrows in a bar.
Read more: Best Christmas movies of the 21st century
Harbour said: "He had become this saccharine version of himself that I think for me was embodied best in those Coca-Cola ads that we still see every year.
"They started I think in the 20s or 30s — this big jolly Santa with rosy cheeks and that beard and those little glasses and the bag on his shoulder.
"It was just that image to me that was so important at the beginning of the film and that he himself was trapped in that image. That wasn't really the guy he was.
"All of these mall Santas — he even meets one at the beginning of the movie — are portraying a version of him that isn't really him. I thought that was really fascinating, so for me it was about the image of Santa Claus."
Read more: Take our Christmas movie quiz
Harbour admitted to feeling some pressure at taking on a Christmas movie, particularly as such a huge fan of the genre.
"It's something that I love to do during Christmas. When I go with my friends to the mall and go shopping and stuff, it's always nice to go and drop in and see a movie in the afternoon," said the 47-year-old.
He added: "To be a part of one of those type of movies, when a lot of my movies are more serious or bigger in a certain way, to be a part of one of those Christmas movies felt very special to me."
Harbour said that Santa was perhaps a more clear-cut good guy than the morally ambiguous heroes he has portrayed in films like Hellboy and Black Widow.
"At least Santa has got a nice and a naughty list that he sticks to and adheres to. That's his code," he said.
Violent Night will be released in UK cinemas on 2 December.
Watch: Trailer for Violent Night