Mortensen is quite the prankster and is known for keeping up good spirits on the set with his practical jokes.
"There’s no sense in doing something, especially if it’s a hard job, if you can’t have a little fun," says Mortensen.
He played a wicked joke on Elijah Wood, his co-star in The Lord of the Rings trilogy. "One time, I called Elijah Wood every day for six weeks pretending to be a long-lost German friend. Most of the calls were in the middle of the night. Fortunately he thought it was funny…," he told Live magazine.
The actor’s shenanigans don’t always end in laughs however. He recalled that one of his jokes quickly degenerated on the set of Lord of the Rings. With the help of Dominic Monaghan, who played Merry Brandybuck, they told producers that the little people starring as the Hobbits in the film were stranded without food or water, on a small island. Producers, in a panic, rounded up everyone’s help to rescue them.