The Uktena

Basic knowledge-

The Horned Serpent appears in the mythologies of many Native Americans.  Details vary among tribes, with many of the stories associating the mystical figure with water, rain, lightning and/or thunder. Horned Serpents were major components of the Southeastern Ceremonial Complex of North American prehistory.

Horned serpents also appear in European and Near Eastern mythology.

In Native American culture-
Rock Art (Pony Hills and Cook's Peak TX)The Horned Serpent was venerated, in various forms, by the Cherokee, Choctaw, Chickasaw, and Creek, just to name a few. Some myths say it is invisible, or that it brought rain and made a noise similar to (but not the same as) thunder.[citation needed]

Among the Eastern and Western Cherokee Indians, the horned serpent known as Uktena was venerated. Anthropologist James Mooney, describes it thus:

"Those who know say the Uktena is a great snake, as large around as a tree trunk, with horns on its head, and a bright blazing crest like a diamond on its forehead, and scales glowing like sparks of fire. It has rings or spots of color along its whole length, and can not be wounded except by shooting in the seventh spot from the head, because under this spot are its heart and its life. The blazing diamond is called Ulun'suti -- "Transparent" -- and he who can win it may become the greatest wonder worker of the tribe. But it is worth a man's life to attempt it, for whoever is seen by the Uktena is so dazed by the bright light that he runs toward the snake instead of trying to escape. As if this were not enough, the breath of the Uktena is so pestilential, that no living creature can survive should they inhale the tiniest bit of the foul air expelled by the Uktena. Even to see the Uktena asleep is death, not to the hunter himself, but to his family."  The Uktena was thought to be able to breathe fire along with its poisonous breathe.  In Cherokee Mythology, the Uktena was created from a common man by "The Little People" to kill the Sun, but the Uktena failed at the attempt and slithered away to another place in the far country.
Horned serpents (rattlesnakes) tied together on a Mississippian sandstone plate from the Moundville Archaeological SiteAccording to Sioux belief, the Unktehila (U?cégila) are dangerous reptilian water monsters that lived in old times. They were of various shapes. In the end the Thunderbirds destroyed them, except for small species like snakes and lizards. This belief may have been inspired by finds of dinosaur fossils in Sioux tribal territory. The Thunderbird may have been inspired partly by finds of pterosaur skeletons.

Other known names-

Misi-kinepikw ("great snake") - Cree
Msi-kinepikwa ("great snake") - Shawnee
Misi-ginebig ("great snake") - Oji-Cree
Mishi-ginebig ("great snake") - Ojibwe
Pita-skog ("great snake") - Abenaki
Sinti lapitta - Choctaw
Unktehi or Unktehila - Dakota

In European iconography-

According to Miranda Green, the snakes reflect the peaceful nature of the god, associated with nature and fruitfulness, and perhaps accentuate his association with regeneration.

Other deities occasionally accompanied by ram-horned serpents include the Celtic Mars (who was a healer rather than a warrior god), the Celtic Mercury, and the Celtic sun-god, Lugh, with whom conventional snakes are also often associated.

In Mesopotamian iconography-

In Mesopotamian mythology Ningishzida, a prototype of the Biblical serpent in the Garden of Eden, is sometimes depicted as a serpent with horns. In other depictions he is shown as human, but is accompanied by bashmu, horned serpents. Ningishzida shares the epithet Ushumgal, "great serpent", with several other Mesopotamian gods.