Michael Fassbender plays two characters and is also one of the producers for Assassin's Creed, a movie based on one of the most successful video game franchises in the gaming world.

Yet neither he, director Justin Kurzel nor co-star and Oscar winner Marion Cotillard had played the game before taking on the project.

So while the multiple storylines and characters in the game might be familiar to legions of players, the film-makers and cast were adamant about coming up with a brand new story that does justice to the complex backstory of the franchise.

"We wanted to start afresh, we wanted to say that this is not a video game, this is a movie," says Fassbender, the 39-year-old Irish-German star behind the X-men trilogy (2011, 2014 and 2016), 12 Years A Slave (2013) and Prometheus (2012).

"The whole thing about taking something from a universe that already exists, you have to respect what's there for sure, but then you have to have a certain amount of disrespect, to bring an element that is ours and what we're creating with the movie."

Speaking to reporters in Sydney, Fassbender, Kurzel and Cotillard say they spent hours learning about the characters and stories from game creators Ubisoft.

Fassbender, in particular, was intrigued by the game's premise of pitting the Assassins, a brotherhood which believes in the protection of free will at all costs, against the Templars, a group that believes in elitism and the evolution of mankind through science and order.

"I thought, wow, that's two really interesting philosophies and through their battle I'm sure we could have a blurring of moralities and there would be something which is not black and white like you find in Star Wars."

He plays the protagonist Callum Lynch, as well as his 15th-century ancestor and assassin, Aguilar de Nerha from the time of the Spanish Inquisition. Through technology that makes use of "genetic memory", his character experiences the memories of the assassin and gains his skills.

Cotillard plays Sofia, a scientist in Abstergo, the organisation behind the technology, and the modern-day version of the Templars.

Fellow Academy Award winner and British actor Jeremy Irons plays her father and Abstergo Industries head Alan Rikkin.

"There is something mysterious about her," says Cotillard, the 41-year-old French actress behind acclaimed movies such as La Vie En Rose (2007), Inception (2010) and The Dark Knight Rises (2012).

"We don't really know where she comes from, we don't really know if she's lived her whole life with her dad. We thought it would be kind of interesting that she didn't have the perfect accent that we could think, 'Oh she has a British dad, so she spent her whole life with him'."

The sci-fi and fantasy world of Assassin's Creed is a huge jump compared to the last time Cotillard, Fassbender and Kurzel worked together, on last year's Macbeth.

The film adaptation of one of Shakespeare's most well-known tragedies received several nominations at the British Independent Film Awards and was in the running for the Palme d'Or at the Cannes Film Festival.

Moving from a moody arthouse flick to a Hollywood sci-fi film is significant for the trio, especially for Kurzel, who is helming his first big-budget production.

"I don't think anything prepares you for doing a film this large. I have an enormous, new-found respect for directors that do make films this large," he says.

"It's been two years of my life, the amount of people that work on it is substantial. I think it's a machine that doesn't move quickly so you've got to be precise and have an enormous amount of endurance to get though the kind of shoot that you have to do for a film like this. It was much bigger than I anticipated."

The film-makers also opted to use as much real stuntwork as they could and film in real-world locations such as Malta, Britain and Spain. Fassbender also did a lot of the stuntwork himself, including one particularly intense horseriding chase scene.

"I'm sick of seeing so much CGI in terms of action sequences, I just kind of get numb to it. When I first saw CGI, I was 'Wow, this is great', but it seems to have just overwhelmed this genre of film-making," he says.

In one particularly memorable scene that mimics the video game trademark, dubbed the Leap Of Faith, stuntman Damien Walters does a 38.1m-high freefall, one of the highest performed by a stuntman in the past 35 years.

Fassbender says: "There's something really thrilling when you see the old films, especially when you see Charlie Chaplin or Buster Keaton, Harold Lloyd. There is something very thrilling about seeing these action sequences with real supporting artists, real stunt people jumping from building to building because you know it's happening for real. It adds a layer of excitement."

The story does not end in this film and Fassbender and Kurzel hope to explore more of the characters as well as have them traverse different time periods for future sequels.

Fassbender says: "That's the part of the process of writing this story - we have an arc for three stories because it's always in threes.

"So you have something that begins here and journeys along and finishes in three and then you start another journey perhaps for another three, but I always like to work in threes like that. We'll see if it happens."

• Assassin's Creed opens tomorrow.