Leviathan was one of the most feared dragons in all the land. He was said to be larger than a mountain (an overstatement), and that he kidnapped young people to use as mates (a lie). Leviathan did, however take it on himself to pluck livestock straight from their pastures and into his waiting claws. A man as large as him did have to eat, after all, dragon or not.
Despite the many stories of his kidnapping young people to use as mates being pure lies, there was one small ounce of truth to them. Maybe young men and women would follow his shadow when he went to hunt. Often, they were looking for a lover or some adventure. In all honesty, he didn’t know. However, it most certainly was not his choice to have these people disappear because of him.