Based on the oldest known written story in a language purporting to be English.
According to Ray Winstone (Beowulf), he and his fellow cast spent several days filming in blue skintight suit, "showing up all your lumps and bumps in all the wrong places. Which can be hard when you're standing in front of Angelina Jolie (Grendel's Mother), who looks stunning in hers."
Crispin Glover and producer and director Robert Zemeckis had previously been on bad terms stemming from the decision to use Glover's likeness in Back to the Future Part II (1989) without his permission, which led to a major lawsuit. The two ultimately reconciled, and Glover agreed to play Grendel.
Model Rachel Bernstein (uncredited) was the body double for Angelina Jolie (Grendel's Mother) in the nude scenes.
According to visual effects supervisor Jerome Chen, close to three hundred cameras were used, compared with sixty-four to seventy-two for The Polar Express (2004).