Aztecs are considered by most experts nowadays as Politeists. This may be true, but as is well known, the religion of the Aztecs was inherited mainly from the Toltecs, whose empire's history still survived in the Anahuac (Valley of Mexico) when the Aztecs, a band of barbarians come from the north, arrived here. At first working as mercenaries in exchange for a place to live, soon the Aztecs fought their own battles that led to the domination of the Anahuac and the largest empire in central Mexico. They picked up the culture of the Toltecs, Teotihuacan, The Totonacas, Zapotecas and even Mayas, lacking a civilization of their own; with this background and absorbing the conquered cultures they finally developed their own distinct civilization.
Though in practice the Aztec religion may have been composed of many Gods, its origin is a Pantheist religion. A single, all-powerful deity was present everywhere and with many aspects. What was later considered deities were actually aspects of the original one, or its agents and helpers.
One factor that helped the idea of politeism is the convenient similarity between the word theos, from the greek god and the word teotl of the aztec language. The spanish used this similarity to their advantage when christianizing the region. The error consists in that teotl actually means wonderful, vast and in some cases terrifying. So the -teotl sufix on many aztec 'deities' doesn't necessarily mean God of Something.
Consider, for example, the catholic religion: it is full of saints; worshipped, shrined, prayed upon. Not to mention the Virgin, angels and other entities. The catholics, though, are not considered to be politheist. The reason for this is that there is a big difference between God, the only deity, and the entities that help him.
Well, according to many experts, this is the case with the religion the Aztecs picked up. There was only one God, or true deity, called Ometeotl (Ome -two and teotl -see above). This god is the father of all the other 'deities' of the aztec pantheon. Actually, mother and father. Ometecuhtli is, literally, Lord of Two or Lord of Duality. He had a feminine aspect, Omecihuatl - Lady of Duality - and many other dual aspects, like good-evil, light-darkness, and creator-destructor. This duality is the source of everything else that exists.
This duality reflects in all the other entities of aztec mysticism, which were never conceived as good or evil. They were neutral. Every one of them had a task, like death or natural forces, and were not ill intentioned towards humans; simply did their jobs no matter what.
To pray for rain, for example, aztecs would turn to Tlaloc - either Ometeotl's water aspect or the natural entity in charge of it. Not actually the God of Waters.
AMAPAN- "Ball Court God" "Patron deity of the Ball"
AMIHMITL- "Chichimec God"
ATLACOAYA- "Pulque God"
ATLATONAN- "Goddess of Lepers"
ATLAUA - "Master of Waters"
CAMAXTLI- "Lord of the Chase"
CENTEOTL (Cinteotl)- "The Corn God"
CHALCHIHUITLICUE- "Goddess of the Sea and Lakes"
CHALMECCACIHUATL- "The Sacrificer"
CHANTICO- "In the House"
CHICOMECOATL- "The Goddess of Sustenance"
CHICONQUIAHUITL- "Seven Rain"
CHIMAMATL- "Shield Hand"
CHIUACOATL- "Woman Snake"
CHIUATETEO- "Celestial Princess"
CHIUHNAUHYOTEUCTLI- "Lord of the Nine"
CHIMALMAN- "One Who Has Sat Like A Shield"
CIPACTONAL- "Calendar God"
CITLALICUE- "God of the Night Sky"
CITLALATONAC- "The Milky Way"
COATLICUE- "Mother of Gods"
COLHUACATZINCATL- "Pulque Deity"
COYOLXAUHQUI- "She with the Belled Cheeks"
COZCAMIAHUATL- "Cornflower Necklace"
CUAUHTLAXAYAUH- "Eagle Face"
CUEXCOCH- "Blue Sky"
HUEHUETEOTL- "Old, Old Deity"
HUITZILOPOCHTLI- "Left Handed Hummingbird" "Hummingbird From The North"
HUIXTOCIHUATL- "Goddess of Water" "Goddess of Salt"
ILAMATECUHTLI- "Old Mother Goddess"
ILANCUEYE- "She of the Old Lady Skirt"
ILHUICAMINA- "He Who Shoots Arrows at the Heavens"
ITZCAQUE- "He Who Has Obsidian Sandals"
ITZLACOHUIHQUI- "Curved Obsidian Knife" "God of Frost"
ITZPAPALOTL- "Obsidian Butterfly"
IXILLAN TONAN- "Goddess of Grass Mountain"
IXPUZTEQUE- "He of the Broken Foot"
IXQUIMILLI- "The Blindfolded One"
IXQUITECATL- "God of Sorcerers"
IXTILTON-"Little Black One"
IZTACMIXCOATL- "Father of Quetzalcoatl and Tezcatlipoca"
MACUILTOTEC- "God of the Arsenal"
MACUILXOCHITL- "Patron of Gambling" "Deity of Flowers"
MATLALCUEYE- "Blue Skirt"
MAYAHUEL- "Goddess of the Maguey Plant"
METZTLI - "The Moon"
MICAPETLACALLI- "The Box of Death"
MICTECACIHUALTL- "Mistress to Mictlantecahtli"
MICTLANTECUHTLI- "The Lord of the Dead"
MIXCOATL (CAMAXTLI)- "Cloud Snake" "Ruler of the Milky Way"
NANAUTZIN - "The Sun"
NAPPATECUTLI- "God of Mat-Makers"
NAUHYOTEUCTLI- "Lord of the Four Directions"
NESOXOCHI- "The One Who Strews Flowers"
NEXTEPEUA-"He Who Rains Ashes"
NOCHPALLI ICUE- "Her Skirt is Prickly Pears"
OMACATL- "Two Reed" "The God of the Feast"
OMECIHUATL- Goddess of Creation" *Female aspect of Ometeotl
OMETEOTL- "Dual Divinity"
OMETECUHTLI-"The Creator God" *Male aspect of Ometeotl
OMETOCHTLI- "God of Pulque"
OZTOTEOTL- "The God of Caves"
PAPAZTEC- "Pulque Deity"
PATECATL-"Pulque God"
PAYNAL- "Messenger God"
PILTZINTECUHTLI-"Youthful God" "The Planet Mercury"
PILIMTEC- "God of Music"
QUETZALCOATL- "The feathered Snake" "God of Wind" "The Creator God" "God of the Evening Star (Venus)"
QUILAZTLI- "She Who Makes Legumes Grow" "Goddess of Childbirth"
TECCIZTECATL - "The Moon God"
TECHALOTL- "Squirrel"
TECHLOTL- "God of the Underworld"
TETEO INNAN-(TOCI)- "Mother of the Gods"
TEPEYOLLOTL- "Heart of the Mountain"
TEUCCIZTECATL- "The Moon"
TEZCATLIPOCA-"The Mirror That Smokes"
TEZCATZONCATL- "Pulque God?"
TLACAHUEPAN- "Younger Brother of Huitzilopochtli"
TLAHUIZCALPANTECUHTLI- "Dawn Lord"
TLACHIHUALTEPETL- "Lord of Many Colors"
TLALCHITONATIUH- "Groundward Sun" "Setting Sun"
TLALOQUE or TEPICTOTON- "Tlaloc's dwarfish attendants"
TLALOC- "The Rain God" "He Who Makes Things Grow"
TLALTECAYOA- "He of the Round Earth"
TLALTECUHTLI- "The Frog Monster" "The Earth-Lord"
TLAZOLTEOL- "The Goddess of Filthy Things"
TLAZOPILLI - "Precious Lord"
TLILPOTONQUI- "Feathered In Black"
TLOQUE NAHUAQUE- "Immanent One"
TONATIUH- "The Sun God" "The Old One"
TONACATEUCTLI-"Agricultural Deity"
TOTEC CHICAHUA- "Our Aged Lord"
TZAPATLAN TENEN- "The Goddess of Turpentine"
TZINTEOTL- "The Goddess of the Rump"
TZITZIMITL-"Demonic Night Creatures"
TZONTEMOC- "He Who Fell Head First"
UAPPATZIN- "Ball Court God"
UIXTOCIHUATL- "Goddess of cultivated foods"
XIPE TOTEC- "Our Lord the Flayed One" "The Skinned One"
XOCHIPILLI- "The Prince of Flowers"
XOCHIQUETZAL- "Flower Quetzal" "Patroness of Erotic Love"
XILONEN- "Tender of the Ear of Corn"
XIPPILLI-"The Jeweled Prince"
XIUHTEUCTLI- Turquoise Lord" "Fire God"
XOLOTL- "The Dog Headed Monster"
YACATECUHTLI- "The Long-Nosed God" "The God of Merchants"
YAOMICQUI- "One Who Has Died at the Hands of the Enemy"
YAUHTECATL- "Pulque God"
YOHUALTONATIUH- "The Night Sun"
YOHUALTICITL- "Midwife of the Night"
ZACAZONTLI- "God of Roads" (adored in Crossroads)