Steve Zahn faced one of his most challenging roles yet in the forthcoming 'War for the Planet of the Apes'. He plays one of Caesar's fellow chimps - who is simply named 'Bad Ape' - and he admits that there was a lot more to it than just moving around like a monkey.

Steve Zahn plays the Bad Ape in 'War for the Planet of the Apes'Steve Zahn plays the Bad Ape in 'War for the Planet of the Apes'

The actor revealed that there were indeed a lot of physical challenges when it came to the role. 'It's extremely physical all day', he confessed. 'To squat, to quadroped, to get up on things and make it look like it's effortless. That's just obvious.'

When you consider what kind of toll it would take on an actor's body to move in that way for hours at a time, your respect certainly grows for the likes of Steve Zahn and his co-stars. However, he also reveals that the physical demands were not the biggest test when it came to playing his character accurately.

Watch the trailer for 'War for the Planet of the Apes' here:

'The hardest thing is probably to find and play the essence of an animal that has a character, that feels, that has perspective', he continues. 'That's the hard part. Playing the essence of an ape. What is that? How is that? I would study film. I would study monkeys; people shooting them with their cameras in zoos just sitting there.'

Sometimes the physical challenges were not about personal strength and endurance, but putting across a certain authenticity, and that's when he's research came into good use. 'Those were the videos that were fascinating to me', he says. 'How do they sit, how do they look? They look over their shoulder differently than we do, how do you reproduce that?'

The film, directed by Matt Reeves, is the third installment of the 'Planet of the Apes' reboot series following on from events in 2014's 'Dawn of the Planet of the Apes'. Apes and the few human survivors are at war for control of the planet and Caesar must make decisions he never wanted to have to make in order to protect and avenge his kind.

More: Watch Steve Zahn's full 'War for the Planet of the Apes' interview

It's Steve Zahn's first appearance in the franchise. Later this year he will appear in the Andrew Haigh drama 'Lean on Pete' and lend his voice in the animated comedy 'Robodog'. He has also completed filming on Ethan Hawke's 2018 Blaze Foley biopic 'Blaze'.

'War for the Planet of the Apes' will be released in theatres on July 14th 2017.