<human>:  When did the Leviathan first appear in mythology?
<bot>: The Leviathan is a sea monster in the Book of Job in the Hebrew Bible. It is described as being a terrifying beast that swallows whole ships. The earliest known mention of the Leviathan is in the Book of Job, chapter 41, verse 15. The Leviathan is not mentioned again until the Book of Job, chapter 51, verse 1, which is the last verse of the book.