agada stories legends - What was/is the leviathan as described in Tanach and Rabbinic literature?

Today the Hebrew word "leviathan" is translated as a whale. But the leviathan of the Tanach seems to be some kind of sea creature. See Job 41:1-34. Tehillim 74 there is an implication that G-d served the meat of the leviathan to the Jews in the Midbar. Isaiah 27:1 describes it as a "tortuous serpent" that G-d will "punish." The Gemara in Bava Basra 74b says that G-d will serve the meat of the leviathan to the righteous. What is the prevailing opinion that best describes the leviathan, taking in these and other treatments of the creature in our texts?