The Leviathan, according to rabbinic literature, was created on the fifth day of creation, along with fish and everything else that lives in the sea. It’s mentioned six times in the Jewish Bible. The longest description appears toward the end of the Book of Job (41:2-26), which describes the Leviathan both physically (“His back has rows of shields…his snorting throws out bolts of light”) and his interactions (“When he rises up, the mighty are terrified…the sword that reaches him has no effect”).
Given all this monster-type talk, one might think that the Leviathan is a vicious killer. However, in the Talmud (Avodah Zarah 3b), we’re given a schedule of what God‘s average day is like–and a full three hours of it is devoted to playing with the Leviathan.