In Korean folklore, an imugi is a serpent-like creature that must live for a thousand years to become a dragon.
Imugi are commonly described as huge, dragon-like serpents that live in water or caves. According to a widespread tradition, an imugi must survive for a thousand years before receiving a magical jewel or pearl called a yeouiju. If successful, it rises and becomes a fully realized dragon, often called a yong.
The story gives the imugi a distinctive place in Korean mythology: it is neither an ordinary snake nor yet a complete dragon. This transformation theme appears in Korean art, folktales, games, and modern fantasy. Some stories portray imugi as benevolent beings seeking heavenly advancement, while others depict them as dangerous or frustrated creatures.
An imugi is not the same as a gumiho, the famous nine-tailed fox, or a haetae, a protective chimera-like guardian. The thousand-year transformation is the key identifying feature.