Mesoamerican culture, as a whole, is often poorly understood among the general populace. Part of it is the fact that the names of the gods are long and hard to pronounce. Part of it is that it's a very complex and, to European sensibilities, insane belief system. Indeed, the whole notion that deities are both good and bad and that all that is created is created as a duality is a very important aspect of pre-Colombian ideology, and something the conquistadors had a hard time wrapping their heads around (as do, to this day, several movie directors. Most importantly, however, it's the sacrifices. Their rich culture and mythological tradition is usually boiled down to "They'd sacrifice people." And, yes, they did practice human sacrifice to a scale and creativity previously unseen by humanity. But this wasn't the only defining feature of the folklore, and, indeed, there was a damn good reason for it.
First of all, let it be known that the Aztecs were never called "Aztecs" in their time. They were known as the Mexica tribe. The various tribes of Central Mexico were generally known as the Nahua, and their language is called Nahuatl meaning "Clear Speech". The Mexica that dominated the valley of Central Mexico at the time of European contact only migrated there sometime in the mid 1200s, from an unknown northern area that they referred to as Aztlán. Much of their culture was adopted from the surrounding tribes that they conquered, such as Toltec and Mayan influences, and filtered through their own tribal values.
When they first arrived in the Central Valley, a number of city-states had been established, and the Mexica wandered around, staying in each city-state earning their keep as mercenaries until they inevitably offended their hosts in some way. In one notable legend, the king of the city-state of Texcoco offered his daughter to the chief of the Mexica as a wife. After they were married, the princess was sacrificed, and her skin was flayed and made into a suit for their high priest. Following this incredible faux pas, the Mexica were banished to a swampy area of Lake Texcoco, with the belief that they'd starve there. According to Mexica myth, their tribe's patron god told them to build a new city on a spot where they'll find an eagle killing a serpent. They saw this happen on top of a prickly pear cactus on a small island way out in the middle of the lake. Undaunted, they began to build the city of Cuauhmixtitlán, Place of the Eagle Between the Clouds, later renamed Tenochtitlán, the Place of the Prickly Pear Cactus (in honor to their first high priest Tenoch), and its twin city Tlatelolco, Place of the Mound of Sand, home of the largest market in the Americas, and thus began the Aztec Empire. Mexico City is there today.
According to the Aztecs, the world was first created by Ometecuhtli/Omecihuatl or "Oemeteotl"  in the singular form, a dual god that was both male and female. Shklee thought the world into existence and gave birth to the first group of major gods.
The most important two gods for the Aztec myths are Quetzalcoatl, the Plumed Serpent, and Tezcatlipoca, the Smoking Mirror. These brothers were two archenemies and most of the Aztec myth revolves around the two of them fighting each other. Quetzalcoatl was the god of wind, dawn, the morning star (aka Venus), knowledge, arts, and crafts. Tezcatlipoca was the trickster god of night, magic, slaves, earth, war, discord, rulership, and a host of others. On different versions they are either the two first brother gods, the elder of the first four brother gods or even the same being in antonym aspects battling with himself, indeed "Black Quetzalcoatl" is a name sometimes given to Tezcatlipoca, and "White Tezcatlipoca" is another name for Quetzalcoatl. Once the Spanish arrived, they marked the two as "good and evil" respectively, but to the Aztec sensibilities, neither of them was necessarily "better" than the other, they were just different and on opposite sides. Most famously, Quetzalcoatl became a human and ruled as a king of Tula, the home of the Toltec people. He was a wise and peaceful ruler who ushered in a golden age... and as a result, none of the other gods were being given tribute. Outraged, Tezcatlipoca came to earth, wormed his way into Quetzalcoatl's council by smooth-talking the right people, winning unwinnable battles, and seducing noblewomen. He managed to get Quetzalcoatl rip-roaring drunk, and as a result, he ended up sleeping with his sister, Quetzalpetlatl. Ashamed, Quetzalcoatl went into self-imposed exile, then killed himself on a funeral pyre, came back to life, and finally sailed east on a raft of snakes, promising to return someday.
Other important gods include the rain god Tlaloc, a monstrous blue creature with goggle eyes, a cleft lip, and jaguar fangs. Tlaloc was one of the oldest gods in Mesoamerica, with analogues dating back to the Olmec civilizations, and he's mostly famous for his child sacrifices. Another was Xipe Totec, the Flayed Lord, the god of fertility, spring, and renewal, also being Red Tezcatlipoca. He represented the maize plant, a golden food wrapped in a husk, so Xipe Totec was a golden god... wrapped in human skin. A tradition that his priests would emulate, killing a sacrificial victim and wearing their skin. Nowhere near last, and not least, was Huitzilopochtli, Left-Handed Hummingbird, the majordomo war god and Blue Tezcatlipoca. Unlike almost every other god listed here, who were venerated throughout Nahua culture, Huitzilopochtli seems to have originated with the Mexica and been brought south with them. And Huitzilopochtli loved his heartburgers. You know the classic image of hundreds of prisoners being brought up an enormous step-pyramid where a high priest would methodically tear their hearts out and raise them to the sky? That was Huitzilopochtli's festival day.
The Nahua Creation myth tells that four worlds existed before the current one:
- The first world, known as the Jaguar Sun, was ruled by Tezcatlipoca, and was populated by a race of giants. These giants were stupid and ate acorns. Tezcatlipoca's sun was black, giving off only half as much light as the others. Quetzalcoatl, enraged, knocked down Tezcatlipoca with a club. Upon falling to the ground, Tezcatlipoca turned into a giant jaguar and ate the world and everyone on it.
- The second world, known as Wind Sun, was ruled by Quetzalcoatl, and was populated by humans. Tezcatlipoca, still enraged, knocked down Quetzalcoatl with a massive jaguar paw. As he fell, the world was destroyed in a massive hurricane. The few humans who survived turned into monkeys.
- The third world, known as Rain Sun, was ruled by Tlaloc. He reigned until Tezcatlipoca stole his first wife, the beautiful flower goddess Xochiquetzal. Furious, Tlaloc gave the people no rain. Drought occurred until Quetzalcoatl overthrew Tlaloc and told him to make it rain. Out of spite, Tlaloc made it rain fire, destroying the world. The humans who survived turned into birds.
- The fourth world, known as Water Sun, was ruled by Chalchiuhtlicue, She of the Jade Skirt, the water goddess and Tlaloc's second wife. Both Quetzalcoatl and Tezcatlipoca were jealous of her, and so they both overthrew her, ending the world in a massive flood. The surviving humans turned into fish.
After the fourth sun was destroyed, the world was completely covered in water. As such, Quetzalcoatl and Tezcatlipoca decided to put aside their grudge to make a new world. See, all the land was on the back of Cipactli, a giant caiman-fish monster, who was chillaxing at the bottom of the ocean. So, to lure it up, Tezcatlipoca lowered his foot to lure it to the surface. After getting it bit clean off, the two gods turned into snakes and strangled Cipactli, thus forming the North American continent.
Now, there was the issue of people. The Aztecs believed that, much like corn seeds grew into new corn plants, human bones would give birth to new humans. So, Quetzalcoatl journeyed into Mictlán, the Aztec underworld alongside Xolotl, a dog-headed lightning god who was Quetzalcoatl's spirit twin. He beseeched Mictlantecuhtli, the Lord of the Dead, to see the bones. Mictlantecuhtli agreed, if Quetzalcoatl could play an acceptable tune on a trumpet, then gave him a conch shell with no holes in it. Quetzalcoatl used worms to bore holes in the shell, then went to see the bones on a strict "look, but don't touch" condition. Quetzalcoatl had Xolotl cause a ruckus while he absconded with the bones. He succeeded, but the deformed Xolotl was unable to escape with him, and thus took the role of Psychopomp, bringing the souls of the dead to their final resting place. Quetzalcoatl ground up the bones and mixed them with his blood, then taking the mix, shaping them into people, and burying them in the ground, cultivating humanity like a crop.
Now, there was the matter of who would be the fifth sun. The gods met on the city of Teotihuacán to decide who would be The Chosen One. Two gods volunteered to become the fifth sun. One was the poor, crippled Nanahuatzin, the other was the rich, beautiful Tecciztecatl. To become the sun, they would have to jump into a fire. Tecciztecatl tried several times, but hesitated each time. Nanahuatzin leapt in without fear and, wanting to save face, Tecciztecatl followed. The two became suns, but the light was too bright and as such, the gods threw a rabbit at Tecciztecatl to diminish his size and his light. Nanahuatzin became Tonatiuh, the solar disk, but the strength of the sun was too great, and as such he had no ability to move across the heavens. The other gods realized that a greater power was needed to move Tonatiuh across the sky.
So, the gods must continuously, to the point of constantly dying and returning to life, give their blood and their hearts to power Quetzalcoatl, in his aspect as Ehecatl, the wind, to send Tonatiuh on his daily path from dawn to dusk. As such, the Aztecs owed an enormous debt to their gods. Quetzalcoatl gave his blood to give humanity new life. The other gods are always giving their blood to allow the sun to rise each morning. They sacrificed many gifts to their gods: incense, chocolate, animals ranging from snakes to eagles to jaguars... but the greatest gift they could give their gods was human blood and human hearts.
Then, a bunch of Spaniards came, following a couple of bad omens (such as a comet, Moctezuma's dream of white people mounted on deer, and the Temple of Huitzilopochtli catching fire). By extreme coincidence, this was around the time that Quetzalcoatl said he would return. Being that they arrived from the east, where Quetzalcoatl went in exile, and that Quetzalcoatl was often envisioned with a beard, Moctezuma was incredibly spooked, and sent the Spaniards gold in hopes they would be satisfied and leave, rather than sending troops to outright kill him. This ambivalence, combined with the fact that the Mexica had a bad reputation among their conquered foes, allowed Cortez to amass an army of natives and enter Tenochtitlan as guests. Things went downhill for the Aztecs from there.
For information on other cultures in the region, see:
- Animorphism: Tezcatlipoca was the most prominent, usually appearing in the form of a jaguar. In this guise, he was called Tepeyollotl, or "Heart of the Mountain," and his roar was believed to cause earthquakes and volcanic eruptions.
- Artificial Limbs: Tezcatlipoca's right foot was replaced with, depending on the version, an obsidian mirror, a snake, or a deer's hoof.
- Beat Still My Heart: Oh, where to begin?
- Badass: Huitzilopochtli.
- Big Badass Bird of Prey: The Aztecs venerated two animals above all others, and one was the golden eagle. Eagles were associated with Huitzilopochtli, the war god, and as such people of high military rank became Eagle Knights, who wore bird costumes.
- Blue and Orange Morality: The Aztec views of what was good and evil were rather alien to the sensibilities to the Spanish conquistadors. Being sacrificed was considered an honor. Indeed, it was the only surefire way to get inducted into the "best" Aztec heaven. Your afterlife was based not on how you lived, but how you died, and none of those afterlives could be considered truly hellish. And, in spite of the war and sacrifices, a lot of Aztec society was pretty progressive. Their treatment of slaves was downright amazing, and they're one of the first societies that had compulsory education for EVERYONE, not just the upper class.
- Bond Creatures: Known as nagual, this was a person's "shadow self," a piece of a person's soul in animal form. Even the gods had these. Quetzalcoatl had Xolotl, the dog-headed god of fire who guided the dead to their resting place.
- Caiman Island: The Aztecs believed the land was created from the corpse of Cipactli, a giant alligator monster.
- Celibate Hero: Quetzalcoatl. Well, at least he USED to be.
- Dem Bones: The common depiction of Mictlantecuhtli is of a skeleton in the regalia of a king.
- Eldritch Abomination: The Tzitzimitl, a group of skeleton women with rattlesnake penises (No, I don't know why they're considered female, that just adds to the Squick). Supposedly, during eclipses, the world was open for them to come down and start wreaking havoc. And there was only one way to prevent that. Go on, guess.
- The End of the World as We Know It: The Aztecs believed that the world we currently live in is actually the FIFTH world. There were four previous worlds destroyed, each with a different god serving as the sun. Our current sun is gonna end with an earthquake. And there's only one way to prevent it.
- Feather Boa Constrictor: Aside from Quetzalcoatl being a literal version of this trope, a few Aztec gods had snakes in their regalia. Tezcatlipoca, in some versions, had a snake as a prosthetic foot. Huitzilopochtli carried a Xiuhcoatl (turquoise fire serpent) as a weapon, using it like a spear-thrower (or possibly a club-sword, seeing that the snake had obsidian studded on it in some depictions)
- Fluffy Cloud Heaven: Tlalocán, run by Tlaloc, the rain god who demanded child sacrifices. This heaven was restricted to people who drowned, were struck by lightning, or died of several illnesses associated with water. This was a cheerful place of eternal springtime and plenty.
- Four Is Death: The journey undertaken to Mictlán, the Aztec underworld, took four years.
- The Great Flood: The end of the Water Sun.
- Hell Hound: Sort of. The Aztecs associated dogs, ALL dogs, with death. Xolotl, the Aztec psychopomp, was represented as a crippled dog-headed human. Additionally, the dead would be buried with a dog, to serve as their guide on their four-year journey to Mictlán.
- A Hell of a Time: Mictlán was the Aztec underworld. There were nine levels, and it took a soul four years to reach its final resting place. The journey was grueling and fraught with peril, but, once you arrived, the land of the dead wasn't so bad. Mictlán was a relaxing, if somewhat dreary place. You spent ten years living there before your soul became a monarch butterfly.
- Hijacked by Jesus: After the Conquest, most of the Aztec gods were demonized, save Quetzalcoatl, who basically became a saint.
- And Coatlicue/Tonantzin, the fertility goddess who gave birth to Huitzilopochtli, got her cult assimilated into the Catholic religion as Our Lady of Guadalupe in order to evangelize the Aztecs. It helped that the Virgin Mary got her church built nearby a hill where the Aztecs used to worship Tonantzin, as well as the supposed apparition to Saint Juan Diego with a lot of Aztec iconography involved.
- In an example of this going somewhere no one really expected, Mictlantecuhtli's wife, Mictecacihuatl, is believed to have evolved over time into Santa Muerte, or "Saint Death." The Mexican archdiocese is not pleased with this, to say the least.
- Hot God: If you didn't look monstrous, you were this. And even then, you usually had some sort of monstrous form
- Human Sacrifice: The Aztecs turned this Up to Eleven. Ripping out hearts of war prisoners on a massive scale was the standard fare. Ceremonies to bring rain required the deaths of crying children (and yes, they HAD to be crying). Harvest festivals involved sacrifice victims being flayed alive and their skins being worn by priests. The "Festival of New Fire" involved a couple being married, then thrown onto a giant bonfire. And that's just the beginning...
- Widely believed to cross over with I'm a Humanitarian: there was a practical reason for all of the sacrifice, after all.
- I Have Many Names: Pretty much every god has a number of different names. In some cases, these come with a change of costume.
- Loads and Loads of Characters: There are over 100 specific deities and supernatural creatures that can be found in the myths.
- Love Goddess: Several.
- Xochiquetzal ("Precious Flower"), goddess of beauty and erotic love
- Xochipilli ("Flower Prince"), Xochiquetzal's twin, god of homosexuality
- Chalchiuhtlicue ("Jade Skirted One"), goddess of chaste love
- Tlazolteotl ("Eater of Filth"), goddess who inspires and forgives sin, particularly sexual sins
- Mayincatec: Averted.
- Moon Rabbit: The gods threw a rabbit at Tecciztecatl to diminish his size and his light, making him the moon instead of the sun.
- Odd Job Gods: A bunch of them. For example, Tlazlteotl, the goddess known as the Sin Eater. And was literally depicted eating sins... represented as feces.
- Only Sane Man: Quetzalcoatl sure seems this way, being the only god to not only do fine without Human Sacrifice, but to outright condemn it.
- Our Dragons Are Different: Quetzalcoatl -- depicted as a winged, feathered serpent -- probably qualifies as this.
- Our Gods Are Greater: Technically, the Aztecs didn't consider the gods "gods" the way Europeans did. Their word for it was "teotl," which indicated a powerful force of nature that did not necessarily have an Anthropomorphic Personification. However, due to the similar nature and the fact that "teotl" sounds like "teolog" (close enough to "teologia", the Spanish word for "theology"), the word became "god."
- Our Monsters Are Weird: Some highlights...
- The ahuitzotl, an otter-dog-monkey water monster that had a hand on its tail and let out a cry like a child, to lure people to the water, whereupon it would drown them and eat their eyes, toenails, and fingernails.
- The Night Axe, a wandering monster resembling a large headless corpse with its chest and belly slit open. Its wound would open and close periodically with a sound like an axe chopping wood. If you came across it while walking at night, you were supposed to approach it fearlessly and, timing it correctly, thrust your hand into the open wound and tear out its heart. If you did this, it would grant you a wish. If you ran away, you would die miserably.
- Then there's the tzitzimeme, star goddesses said to harrow the world during a solar eclipse. They're beautiful women with skeletal faces and rattlesnakes for penises. Yes, they're distinctly female, and they have rattlesnakes for dicks.
- Owl Be Damned: Owls were the Aztec symbol of death, and associated with Mictlantecuhtli.
- Panthera Awesome: Aztecs venerated the jaguar as king of the beasts, and high ranking military officials could become Jaguar Knights. Tezcatlipoca was represented by a jaguar, as were a few other gods of the Aztecs and surrounding cultures.
- Jaguars caused The End of the World as We Know It (well, the first one... we are living in the fifth world).
- Pet the Dog: Tezcatlipoca was the god of slaves. Indeed, one of his names is "He whose slaves we are." As such, Tezcatlipoca severely punished anyone who mistreated their slaves.
- Psychopomp: Xolotl.
- Razor Wings: A goddess called Itzapapalotl (the Flint Lock Butterfly, who was the ruler of the afterlife for sacrificed babies, among other things) could appear as a skeletal warrior goddess with butterly wings made out of obsidian knives.
- Religion of Evil: To most non-Aztecs this is what the Aztec beliefs where.
- Somewhere a Paleontologist Is Crying: Possibly averted; they certainly liked their feathered reptile iconography. Maybe they knew something it's taken us centuries to work out?
- Lampshaded in the short-lived Godzilla animated series when the team discover a giant archaeopteryx which may have inspired the Quetzalcoatl ("Q") myths.
- Skull for a Head: Cihuacoatl and Mictlantecuhtli.
- Springtime for Hitler: When in Tula, many people tried to sabotage Tezcatlipoca's attempts to worm his way into the upper crust, but all these attempts failed. One such attempt is when he was sent into battle commanding a legion of hunchbacks and dwarfs. He won anyway.
- Top God: There's little consensus as to who actually rules the pantheon. Huitzilopochtli, as the Mexica's patron, usually gets this role, thanks to Spanish translations. Others place Tezcatlipoca as this role, others Tonatiuh. Usually it depends on who you're asking and which city-state they came from.
- Trickster Archetype: Tezcatlipoca, again.
- The Unpronounceable: While Mexica names aren't actually that hard to say if you hear them, they sure look unpronounceable.
- War God: Several, but particularly Huitzilopochtli, who is all about this. Tezcatlipoca has shades of this, but he's more about the chaos brought on by war than war itself.
- But see the hottips for some quick-and-dirty help. Really, the names aren't so bad, once you get the hang of them--take it one syllable at a time, use Spanish phonemes, and remember that (as in Spanish) the accent usually falls on the penultimate syllable unless there's an accent mark, in which case the accent falls there instead.
- "oh-meh-teh-KOOT-lee" / "oh-meh-see-WAT-ull"
- "SHEE-peh TOW-tek"