One of four creatures associated with the cardinal directions in Chinese mythological cosmology, the Xuanwu, (“dark warrior,” sometimes translated as “black warrior”) is a chimera-like hybrid animal with the head and tail of a snake and the body of a tortoise.
Unrelated to the twelve creatures of the Chinese zodiac, these four creatures each has its signature color, season, element, celestial quadrant, and other features: Green or Blue Dragon of the East (Qinglong: spring, water), Red Phoenix of the South (Zhuque: summer, fire), White Tiger of the West (Baihu: autumn, metal), and Dark Warrior of the North(Xuanwu: winter, earth). The fifth direction—that is, the center of the universe—in this cosmological map is China itself.
The origin of the cardinal-direction creatures is said to date back to the Warring States period (475–221 B.C.E.) and the Han dynasty (206 B.C.E.–220 C.E.).
Other Chinese legends also speak of how the "Tortoise General" and a "Snake General" came to be. During Xuánwǔ's study to achieve enlightenment and god status he was told that in order to fully achieve god status, he must purge all humanly flesh from his body. Since he was born he had been eating the food of the world, humanly food, therefore his stomach and intestines were still human. Legend told of an event that a god came and changed out his human stomach and intestines for a godly body so he could fully achieve god status. (It was also said that the stomach and intestines that were tossed out became the "Tortoise Mountain" and "Snake Mountain".) The stomach and intestines taken out by the god who did the surgery on Xuánwǔ were said to have taken on the shape of a tortoise (stomach) and a snake (intestines). As many Chinese legends speak of certain animals becoming demons over time as they gain knowledge, that's what the tortoise and snake became, and terrorized people. As Xuánwǔ, now in his god status, heard of this, he came and slayed the demons from his past. However, he did not kill them, as the snake and tortoise demons showed remorse. He let them train under him and atone for their wrong doings, and they became the "Tortoise General" and "Snake General", and they assisted Xuánwǔ with his quests.
According to another source, once Xuánwǔ's had begun study of the way, he discovered that he must purge himself of all his past sins to become a god. He learned to achieve this by washing his stomach and bowels (intestines) in the river. In the washing of his internal organs, his sins melted from them and into the river in a dark, black form. These then formed into a black tortoise and snake who terrorized the people. Once Xuánwǔ learned of this, he returned to conquer the forms of this past sins and subdue them under himself and they became his servants.