Since he planned to use a real elephant for some of the footage in the zoo, Ray Harryhausen asked for one that was 15 feet tall, but the film was only able to procure an eight-foot-tall one for him. In order to make the elephant look much bigger, a 4'6" actor was cast to play the zookeeper.
Though the creature is referred to as the Ymir in reviews and websites, the name is never mentioned in the movie. Ray Harryhausen was concerned that audiences would mistake it for the Arabic title "Emir".
Ray Harryhausen's original design for the monster was a giant cyclops, similar to the one he later used in The 7th Voyage of Sinbad (1958). He discarded the idea after making a clay model of it, and eventually settled on the reptilian Ymir.