The term "Mespotamian mythology" covers the ancient religions of Sumer, the Akkadian Empire, Assyria and Babylon. Obviously, Mespotamia figures heavily in the Bible; Abraham and his kin were, mostly likely, natives of the Sumerian city of Ur.
Sumer, as you might have learned in your World History classes, is probably the oldest human civilization, that flourished from the 5th to the 3rd milennia BCE. Sumer began and ended as a collection of city-states in what is now Iraq. It's usually assumed that Sumerians were responsible for the invention of year-around agriculture, writing, the wheel, irrigation, and beer. Since the Sumerian language has no known cognates, it's anyone's guess where they came from. Some writers take this a step further and argue that the Sumerians were either assisted by aliens or aliens themselves.
In the 3rd millenia BC, Sumer began to decline. Like the collapse of any superpower, there were a lot of reasons for this, but the primary reason, it seems, is that they were just plain displaced by Akkadians and various other Semitic people. After Sumer's decline, it was displaced by the Akkadian Empire, who borrowed the Sumerians' gods in the way that the Romans borrowed the Greek gods. The Akkadian Empire was not as fortunate as Sumer had been, though, and its rule collapsed after about a century. But the Akkadians proved to be a plucky lot, and they managed to recoup and build new cities. They kept this up until they were all conquered in 539 BCE by the Persians, which rendered the whole thing pretty moot.
Studying Mesopotamian mythology in general is a little bit easier than studying most Indo-European mythologies, because the Mesopotamians were literate, but even so, there's a lot of conflicting information. The most likely reason is simple evolution of the religion as time went on.
Major characters of Mesopotamian Mythology include:
- Anu, god of heaven and the stars.
- Enlil (Ellil) The god of wind and the sky. Often identified with Jupiter.
- Enki (Ea) The god of water and wisdom. Enki was much more fond of humanity than most other gods and was generally a pretty groovy guy. Often identified with Mercury.
- Ishkur (Adad), god of storms. He is either the brother of Enki or a son of Nanna and Ningal.
- Nammu, (Tiamat) goddess of the primeval waters.
- Ki, goddess of the earth.
- Ninhursag (Ninmah, Nintu, Mamma, Aruru, Belet-Ili), goddess of nature and earth, and the wife of Enki. May or may not be the same as Ki, above.
- Ninlil (Sud, Mulittu), the wife of Enlil and usually the mother of Nanna, Nergal, Ninazu, Ninurta and Enbilulu.
- Nanna (Suen, Sin), god of the moon. His wife is Ningal, goddess of the reeds.
- Nergal, god of fire, destruction, war, plagues, and occasionally, the sun. Often identified with Mars.
- Ninurta, god of agriculture, healing and destruction. Often identified with Saturn.
- Ereshkigal (Allatu, Irkalla), the ruler of the underworld, older sister of Inanna and wife of Nergal. They're the daughters of either Anu or Nanna.
- Inanna (Ishtar, Inana), goddess of warfare, love, and fertility. Often identified with Venus.
- Utu (Shamash), god of justice and the sun, son of Nanna and Ningal.
- Marduk, water, vegetation, judgment and magic; son of Enki and Damkina. As the patron deity of Babylon who was created to justify the Babylonians' dominance, you could call him an Ur Example of a Marty Stu.
- Exclusively Evil: The Allu, Asakku, Gallu and Rabisu
- Back from the Dead: Dumuzi, Inanna's husband, in a Just-So Story about the origin of the seasons.
- Belligerent Sexual Tension: The courtship of Ereshkigal, Queen of the Netherworld and Nergal, god of plagues and fire.
- Blow You Away: Enlil, god of wind and air. Also Ishkur, god of storms.
- Bottle Fairy: Ninkasi, Siris and Siduri, goddesses of beer.
- Canon Immigrant: Many religious scholars believe that Inanna, due to the difficulty in deciphering the origin of her name, her constantly changing parentage, and the fact that she explicitly had no responsibilities at first, was originally a Proto-Euphratean goddess incorporated into the Sumerian pantheon.
- Chickification: Can be observed from looking at the oldest Sumerian myths to its later derivatives. One example is Nammu, who went from the sole creator goddess in Sumerian myths to her more well-known Babylonian version Tiamat, a co-creatrix who after the death of her husband became a tyrant who is probably the Ur Example of God Save Us From the Queen. Sumerian Ereshkigal was the sole ruler of the underworld, but in later Assyro-Babylonian myths she was subdued by Nergal and forced to cede her power to him. Several other goddesses known to us mainly as Shallow Love Interests are also believed to have held more prominent roles in prehistory.
- Child Eater: Dimme and Dimme-kur (Akhkhazu). Sometimes Lilitu as well.
- Copy Cat Stu: In the lost Sumerian version of Enuma Elish, Enlil was probably responsible for vanquishing Nammu/Tiamat. In the Babylonian version, this honor was given to Marduk.
- Cosmic Close Call: A Babylonian myth recorded in the Talmud and transcribed by W. Somerset Maugham tells of a merchant in Baghdad who sent his servant to the marketplace for provisions, only for the servant to come home white and trembling. The servant was jostled by a woman whom he recognized as Death, and fled to Samarra to hide from her after she makes a threatening gesture. The merchant later finds Death at the market place to inquire about the threatening gesture, and she replies:
“That was not a threatening gesture, it was only a start of surprise. I was astonished to see him in Baghdad, for I have an appointment with him tonight in Samarra.”
- Crapsack World: Humans were created to be slaves to the gods and when they died, they all went to the same gloomy underworld. Any wonder why their scribes wrote stuff like this:
"Tears, lament, anguish, and depression are within me. Suffering overwhelms me. Evil fate holds me and carries off my life. Malignant sickness bathes me."
- Dark Is Not Evil: Though moody and demanding, most of the gods of the Netherworld weren't really evil, per se.
- Death by Sex: Happens to all of Inanna's lovers eventually. This is why Gilgamesh turns her down.
- Divine Parentage: The only humans who figure at all in the myths have this.
- Draconic Divinity: Tiamat is the goddess of the primordial sea, and the mother of many creatures including dragons. She's also frequently portrayed as a dragon herself, though there's no true "canonical" description of the form she took.
- Eldritch Abomination: Though often described as dragons, Tiamat, Apsu, Kingu and Mummu fit this trope much better.
- Evil Versus Evil: The demon, Pazuzu was often invoked to ward off Dimme.
- Expy: Inverted. The Greek goddess, Aphrodite, is usually assumed to an expy of Astarte, a Canaanite version of Inanna.
- Ereshkigal herself appears to be an underworld expy of her twin, Inanna (and some believe they may have even been the same goddess at one point!)
- Femme Fatale: Inanna, of course.
- The Glorious War of Sisterly Rivalry: Inanna and Ereshkigal
- The Great Flood: Possibly the Trope Maker
- Hermaphrodite: Depending on the Writer, the supreme god, Anu, was sometimes portrayed as this.
- Horny Devils: Lilitu, Dimme and Dimme-kur were sometimes portrayed this way as well.
- I Have Many Names: Nearly all of the gods, which was somewhat inevitable when their worshipers spoke a variety of languages.
- Jerkass Gods: Indeed.
- Les Yay: Inanna and Ninshubur, full stop.
- Loads and Loads of Characters: There were about six main gods and hundreds of minor, local deities.
- Lovable Sex Maniac: Enki had the rather disturbing habit of seducing his own (grand)daughters, but was usually one of the friendlier and more good-natured gods.
- Making a Splash: Enki, god of rivers and lakes. Also his daughter, Nanshe.
- Mister Seahorse: In the myth of Enki and Ninhursag, Enki becomes pregnant after consuming his own semen.
- Mix-and-Match Critters: Aqrabuamelu (scorpion men), Shedu (winged lions and bulls), Sirrush (dragon-like creature with eagle talons and the forelegs of a cat), Zu (eagles with lion heads)
- Offing the Offspring: Apsu and later Tiamat attempt this in the Enuma Elish. It doesn't work out.
- Our Demons Are Different: Most Middle Eastern demons in general are flat-out nasty, though they can Pet the Dog now and then.
- Our Ghosts Are Different: Classified as Alû, Edimmu or Gidim; they were usually not very nice.
- Our Giants Are Bigger: Humbaba, among others.
- Parental Incest: A bit of that, yes.
- Rape Is Love: Probably Values Dissonance in action; the god, Enlil raped the maiden, Sud (later Ninlil). He was punished for it by being exiled to Irkalla, but she followed him into exile and later, married him and had some more children with him.
- Servant Race: Humanity were explicitly created to be slaves to the gods.
- Shallow Love Interest: Many goddesses (Aya, Sarpanit, etc.) have little-to-no roles outside of being some god's wife.
- She's a Man In Japan: Inverted. Inanna's second-in-command, Ninshubur, is female in the Sumerian myths, but was turned into a male in the later Assyro-Babylonian versions.
- Sibling Yin-Yang: Among others, Utu and Nergal.
- Slap Slap Kiss: The Courtship of Inanna and Dumuzi
- Star-Crossed Lovers: Inanna and Dumuzi
- The Nothing After Death: The Mesopotamian Netherworld, Irkalla, was not a happy place.
- To Hell and Back: Inannas Descent to The Netherworld is an Ur Example, if not the Trope Maker.
- Tsundere: Inanna was usually Type A.
- She also seems to cross over into Yandere territory
- The Vamp: Lilitu, who was ordered by the gods to attempt to lead men astray.
Works that reference and/or derive from Mesopotamian mythology
- The Courtship Of Inanna And Dumuzi
- Inannas Descent to The Netherworld
- Cthulhu Mythos (sort of)
- Fate/stay night and its franchise.
- Enuma Elish
- The Epic of Gilgamesh
- Storm Constantine's Grigori Trilogy
- Snow Crash
- Clive Barker's Jericho, in which you battle Ninlil, Ki, Inanna, Enlil, Nanna and Utu
- Least of all the five-headed multihued version from Dungeons & Dragons.