The Ouroboros is a self-cannibalizing snake.

The Ouroboros is a serpent, or sometimes a dragon, that eats its own tail. It is a representation of the cyclical nature of life and the universe, eternity, an endless cycle and transforming that which it has ended into something new. It is an important symbol in religion and mythology but was also frequently used in alchemic illustrations as a symbol of the circular nature of alchemists’ opus, the search for the Philosopher's Stone. The Ouroboros was also associated with the yin yang symbol because half of its body was depicted as dark while the other half was light.

The name Ouroboros is Greek in origin but it dates back to Ancient Egyptian times. A picture of the Ouroboros is in the Egyptian Book of the Netherworld. Though what is written about it is still unknown because no one can translate what is written. In the Book of the Dead, the sun god Atum ascended from the chaotic waters in the form of a snake that renewed itself every morning. From Egypt, the idea of a tail eating dragon passed into Phoenicia and then into Greece where scholars gave it its name.

The philosopher Plato described the Ouroboros as the first living thing in the universe. He said that it had no need of eyes because there was nothing to see, it did not have ears because there was nothing to be heard and because there was not an atmosphere to breathe, it did not have any organs. Plato said that it was an immortal, perfectly constructed being, his own ways provided him food, and all he did or suffered was because of himself. It had no hands because it had no reason to take anything or defend himself against anyone. Nor did he have feet for he had no reason to move beyond his revolving circle.

The Ouroboros imagery has been used in India to describe Kundalini energy. Kundalini energy is the dormant potential of the human. It is said to lie at the base of the spine like a snake coiled upon itself with its tail in its mouth. In Hindu mythology, the Ouroboros is a dragon that circles a tortoise, which supports the four elephants that carry the world.

In Norse mythology, the serpent Jormungand is a child of the god Loki. Odin kidnapped him and threw him into the ocean. He stayed here where he slept and ate so much that he encircled the world until he could bite his own tail. He became known as the World Serpent or the Midgard Serpent. In another story, a king gives his daughter a small lindworm. The lindworm grew into a large serpent that encircled the girl’s bower and bites its own tail. The serpent is slain by Ragnar Lodbrock marries the princess.

The Ouroboros appeared in 14th and 15th century Albigensian printing watermarks, subtle image put on paper to show where it was made. The image of the Ouroboros was also worked into playing cards and tarot cards. It was commonly used to encircle the chalice on the Ace of Cups for tarot decks. In the early 1900s, the Magician in a Rider Waite Smith tarot deck has an Ouroboros around his waist instead of a belt.

The Ouroboros was adopted by Christianity to symbolize the limited confines of the material world. It was also used to symbolize the self-consuming, self-defeating, and circular nature of this world’s existence.

A Swiss psychologist named Carl Jung described the Ouroboros is an archetype and a sigil of alchemy. A drawing of the Ouroboros from a 2nd century alchemical text encloses the words hen to pan "one is the all". One half of it is black and the other half is white representing the tool nature of existence. It is a symbol of the cycle of birth and death from which alchemists sought release.