Bouddhism

• The Vinaya (ii.109) contains a list of four royal families of Nāgas (Ahirājakulāni): Virūpakkhā, Erāpathā, Chabyāputtā and Kanhagotamakā. Two other Nāga tribes are generally mentioned together: the Kambalas and the Assataras. It is said (SA.iii.120) that all Nāgas have their young in the Himālaya.
• The best known of all Nāgas is Mahākāla, king of Mañjerika-bhavana. He lives for a whole kappa, and is a very pious follower of the Buddha. The Nāgas of his world had the custodianship of a part of the Buddha's relics till they were needed for the Māha Thūpa (Mhv.xxxi.27f.), and when the Bodhi tree was being brought to Ceylon they did it great honour during the voyage (Mbv. p.. 163f.). Other Nāga kings are also mentioned as ruling with great power and majesty and being converted to the Buddha's faith - e.g., Aravāla, Apalālā, Erapatta, Nandopananda, and Pannaka. (See also Ahicchatta and Ahināga.) In the Atānātiya Sutta (D.iii.198f.), speaking of dwellers of the Cātummahārajika world, the Nāgas are mentioned as occupying the Western Quarter, with Virūpokkha as their king.
• The Nāgas had two chief settlements in Ceylon, in Nāgadīpa (q.v.) and at the mouth of the river Kalyānī. It was to settle a dispute between two Nāga chiefs of Nāgadīpa, Mahodara and Cūlodara, that the Buddha paid his second visit to Ceylon. During that visit he made a promise to another Nāga-king, Manjakkhika of Kalyānī, to pay him a visit, and the Buddha's third visit was in fulfilment of that undertaking (Mhv.i.48f.).
• The Nāgas form one of the guards set up by Sakka in Sineru against the Asuras (J.i.204). The Nāgas were sometimes worshipped by human beings and were offered sacrifices of milk, rice, fish, meat and strong drink (J.i.497f.). The jewel of the Nāgas is famous for its beauty and its power of conferring wishes to its possessor (J.vi.179, 180).
• The word Nāga is often used as an epithet of the Buddha and the Arahants, and in this connection the etymology given is āgum na karotī ti Nāgo (e.g., MNid.201). The Bodhisatta was born several times as king of the Nāgas: Atula, Campeyya, Bhūridatta, Mahādaddara, and Sankhapāla.

In the accounts given of the Nāgas, there is undoubtedly great confusion between the Nāgas as supernatural beings, as snakes, and as the name of certain non Aryan tribes, but the confusion is too difficult to unravel.

Hindhuism

The Nagas according to Hinduism include Manasa, Mucilinda, Shesha and Vasuki  

• In Hinduism, Manasa is a naga and goddess of fertility. She is venerated in eastern India for protection against snakebite.
• In Hinduism and Buddhism, Mucalinda is a naga, a snake-man, who protected the Buddha from the elements before his enlightenment.
• It is said that four weeks after Gautam Buddha began meditating under the Bodhi tree, the heavens darkened for seven days, and a prodigious rain descended. However, the mighty king of serpents, Mucalinda, came from beneath the earth and protected with his hood the one who is the source of all protection. When the great storm had cleared, the serpent king assumed his human form, bowed before the Buddha, and returned in joy to his palace.
• According to Hindu (Vedic) tradition, Shesha is an expansion of Vishnu who takes the form of a gigantic Divine Serpent (naga) with many thousands of heads. In the Puranas He is said to hold all the planets of the universe on His hoods and to constantly sing the glories of Vishnu from all His mouths.
• Vasuki is a naga, or one of the serpents of Hindu mythology. He is also the king of the nagas and has a gem (Nagamani) on his head. Manasa, another naga is his sister.
  
  Legends of Vasuki

The most famous legend in Hinduism that Vasuki takes part in was when the incident churning the ocean of milk. He agreed to allow the devas (gods) and the asuras (demons) use him as the churning rope, bound with Mount Meru when they churned the ocean of milk for the ambrosia of immortality. While Vasuki was being used as a rope, he was feeling a lot of strain and pain. This strain caused him to exhale Alahala, the most potent venom in the universe. There was the danger that the Alahala could destroy all living beings and perhaps the universe itself. Then Shiva, in order to prevent the destruction of the cosmos, decided to swallow the poison himself. However, instead of swallowing the poison completely he left it in his throat, turning his throat blue and earning him the title Nilakanta (blue-throated).
For Malay sailors, nagas are a type of dragon with many heads; in Thailand and Java, the naga is a wealthy underworld deity. In Laos they are beaked water serpents.