Nāga is the Sanskrit and Pāli word for a deity or class of entity or being who takes the form of an enormous snake—specifically the king cobra. The Nāga is found in Hinduism, Buddhism, and Jainism. A female Nāga is called a nāgīor nāgiṇī.

The creatures have variously been depicted as negative or evil, as persecutors of all other creatures, and as virulent, poisonous snakes of great prowess and strength. Their physical characteristics vary somewhat, ranging from mostly serpent-like to somewhat anthropomorphic. In Hinduism, however, the creatures are said to be snakes who may take human form at will. They are inquisitive and tend to be malevolent, but only when mistreated. They are associated with rivers, lakes, seas, and wells, and have come to be known as guardians of certain treasures.

In some parts of the world, the Nāga is altogether holy, objects or creatures of reverence—for example, in South India, where is it believed that they bring fertility and prosperity. In other parts of the world, they are believed to hold the key to immortality and youth. Extravagant rituals are conducted in their honor, and whole communities believe they are ethnically or ancestrally linked to the creatures.