A Leviathan is a sea monster referenced in the Tanakh, or the Old Testament. The word has become synonymous with any large sea monster or creature, including the more specific term of Kraken. In literature it refers to great whales, and in Modern Hebrew, it means simply 'whale'.
Ancient Middle Eastern: Sea serpents feature prominently in the mythology of the Ancient Near East, attested as early as the 3rd millennium BCE in Sumerian iconography depicting the myth of the god Ninurta overcoming the seven-headed serpent. Examples of the storm god vs. sea serpent trope in the Ancient Near East can be seen with Baʿal vs. Yam (Canaanite), Marduk vs. Tiamat (Babylonian), and Atum vs. Nehebkau (Egyptian) among others, with attestations as early as the 2nd millennium as seen on Syrian seals.
Christianity: The Leviathan of the Middle Ages was used as an image of Satan, endangering both God's creatures—by attempting to eat them—and God's creation—by threatening it with upheaval in the waters of Chaos. St. Thomas Aquinas described Leviathan as the demon of envy, first in punishing the corresponding sinners (Secunda Secundae Question 36). Leviathan became associated with, and may originally have referred to, the visual motif of the Hellmouth, a monstrous animal into whose mouth the damned disappear at the Last Judgement, found in Anglo-Saxon art from about 800, and later all over Europe
Satanism: In LaVeyan Satanism, according to the author of The Satanic Bible, Anton Szandor LaVey, Leviathan represents the element of Water and the direction of West. The element of Water in Satanism is associated with life and creation, and may be represented by a Chalice during ritual. In The Satanic Bible, Leviathan is listed as one of the Four Crown Princes of Hell. This association was inspired by the demonic hierarchy from The Book of the Sacred Magic of Abra-Melin the Mage. The Church of Satan uses the Hebrew letters at each of the points of the Sigil of Baphomet to represent Leviathan. Starting from the lowest point of the pentagram, and reading counter-clockwise, the word reads "לִוְיָתָן". Translated, this is (LVIThN) Leviathan. In Demonology, the Leviathan is one of the seven princes of Hell (envy) and its gatekeeper.
Jewish: Rashi's commentary on Genesis 1:21 repeats the tradition: "God created the great sea monsters—taninim. According to legend this refers to the Leviathan and its mate. God created a male and female Leviathan, then killed the female and salted it for the righteous, for if the Leviathans were to procreate the world could not stand before them." In the Talmud Baba Bathra 74b it is told that the Leviathan will be slain and its flesh served as a feast to the righteous in [the] Time to Come, and its skin used to cover the tent where the banquet will take place. The festival of Sukkot (Festival of Booths) therefore concludes with a prayer recited upon leaving the sukkah (booth): "May it be your will, Lord our God and God of our forefathers, that just as I have fulfilled and dwelt in this sukkah, so may I merit in the coming year to dwell in the sukkah of the skin of Leviathan. Next year in Jerusalem."
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The enormous size of the Leviathan is described by Johanan bar Nappaha, from whom proceeded nearly all the aggadot concerning this monster: "Once we went in a ship and saw a fish which put his head out of the water. He had horns upon which was written: 'I am one of the meanest creatures that inhabit the sea. I am three hundred miles in length, and enter this day into the jaws of the Leviathan'"
The body of the Leviathan, especially his eyes, possesses great illuminating power. This was the opinion of Rabbi Eliezer, who, in the course of a voyage in company with Rabbi Joshua, explained to the latter, when frightened by the sudden appearance of a brilliant light, that it probably proceeded from the eyes of the Leviathan. He referred his companion to the words of Job xli. 18: "By his neesings a light doth shine, and his eyes are like the eyelids of the morning". However, in spite of his supernatural strength, the leviathan is afraid of a small worm called "kilbit", which
