Excerpted from Wikipedia:
The Nāga (IAST: nāga; Devanāgarī: नाग) or Nagi (f. of nāga; IAST: nāgī; Devanāgarī: नागी) are divine, semi-divine deities, or a semi-divine race of half-human half-serpent beings that reside in the netherworld (Patala) and can occasionally take human form. Rituals devoted to these supernatural beings have been taking place throughout south Asia for at least two thousand years. They are principally depicted in three forms: wholly human with snakes on the heads and necks, common serpents, or as half-human half-snake beings in Hinduism, Buddhism and Jainism. A female naga is a “Nagi”, “Nagin”, or “Nagini”. Nagaraja is seen as the king of nāgas and nāginis. They are common and hold cultural significance in the mythological traditions of many South Asian and Southeast Asian cultures. They are the children of Rishi Kashyapa and Kadru.
In Sanskrit, a nāgá (नाग) is a cobra, the Indian cobra (Naja naja). A synonym for nāgá is phaṇin (फणिन्). There are several words for “snake” in general, and one of the very commonly used ones is sarpá (सर्प). Sometimes the word nāgá is also used generically to mean “snake”. The word is cognate with English ‘snake’, Germanic: *snēk-a-, Proto-IE: *(s)nēg-o- (with s-mobile).
The mythological serpent race that took form as cobras can often be found in Hindu iconography. The nāgas are described as the powerful, splendid, wonderful and proud semidivine race that can assume their physical form either as human, partial human-serpent or the whole serpent. Their domain is in the enchanted underworld, the underground realm filled with gems, gold and other earthly treasures called Naga-loka or Patala-loka. They are also often associated with bodies of waters — including rivers, lakes, seas, and wells — and are guardians of treasure. Their power and venom made them potentially dangerous to humans. However, they often took beneficial protagonist role in Hindu mythology; in Samudra manthan folklore, Vasuki, a nāgarāja who abides on Shiva’s neck, became the churning rope for churning of the Ocean of Milk. Their eternal mortal enemies are the Garudas, the legendary semidivine birdlike-deities.
Vishnu is originally portrayed in the form sheltered by Śeṣanāga or reclining on Śeṣa, but the iconography has been extended to other deities as well. The serpent is a common feature in Ganesha iconography and appears in many forms: around the neck, use as a sacred thread (Sanskrit: yajñyopavīta) wrapped around the stomach as a belt, held in a hand, coiled at the ankles, or as a throne. Shiva is often shown garlanded with a snake. Maehle (2006: p. 297) states that “Patanjali is thought to be a manifestation of the serpent of eternity”.
As in Hinduism, the Buddhist nāga generally has sometimes portrayed as a human being with a snake or dragon extending over his head. One nāga, in human form, attempted to become a monk; and when telling it that such ordination was impossible, the Buddha told it how to ensure that it would be reborn a human, and so able to become a monk.
The nāgas are believed to both live on Nagaloka, among the other minor deities, and in various parts of the human-inhabited earth. Some of them are water-dwellers, living in streams or the ocean; others are earth-dwellers, living in caverns.
The nāgas are the followers of Virūpākṣa (Pāli: Virūpakkha), one of the Four Heavenly Kings who guards the western direction. They act as a guard upon Mount Sumeru, protecting the dēvas of Trāyastriṃśa from attack by the asuras.
Among the notable nāgas of Buddhist tradition is Mucalinda, Nāgarāja and protector of the Buddha. In the Vinaya Sutra (I, 3), shortly after his enlightenment, the Buddha is meditating in a forest when a great storm arises, but graciously, King Mucalinda gives shelter to the Buddha from the storm by covering the Buddha’s head with his seven snake heads. Then the king takes the form of a young Brahmin and renders the Buddha homage.
In the Vajrayāna and Mahāsiddha traditions, nāgas in their half-human form are depicted holding a nāgas-jewel, kumbhas of amrita, or a terma that had been elementally encoded by adepts.
The two chief disciples of the Buddha, Sariputta and Moggallāna are both referred to as Mahānāga or “Great nāga”. Some of the most important figures in Buddhist history symbolize nāgas in their names such as Dignāga, Nāgāsēna, and, although other etymons are assigned to his name, Nāgārjuna.
The Nāga Saṃyutta of the Pali Canon consists of suttas specifically devoted to explaining nature of the nāgas.
In the “Devadatta” chapter of the Lotus Sutra, the daughter of the dragon king, an eight year old longnü (龍女, nāgakanyā), after listening to Mañjuśrī preach the Lotus Sutra, transforms into a male Bodhisattva and immediately reaches full enlightenment. Some say this tale appears to reinforce the viewpoint prevalent in Mahayana scriptures that a male body is required for Buddhahood, even if a being is so advanced in realization that they can magically transform their body at will and demonstrate the emptiness of the physical form itself. However many schools of Buddhism and classical, seminal Chinese exegeses interpret the story to repudiate this viewpoint, stating the story demonstrates that women can attain Buddhahood in their current form.
According to tradition, the Prajñapāramita sutras had been given by the Buddha to a great nāga who guarded them in the sea, and were conferred upon Nāgārjuna later.
I have often pondered on the similarity of nāga with nagal and nagual, East meets West.
Gateway to the Nagual’s world similar to Nagaloka?