Nagas are The Serpent Kings

In Hinduism, nagas are a primeval race of divine serpent-people that play an important part in religion. They are half-human and half snake, and are still worshipped as the bringers of fertility, especially in southern India. They are the guardians of rain, and thus fertility, but are also thought to bring disasters such as floods and drought. They are the protectors of springs, wells and rivers.

As the guardians of rain, you can see statues of the Buddha meditating where a seven-headed serpent has spread its hood over the Buddha's head to protect him from the rain.

Their ruler is the seven-hooded Sesha, and Vishnu is often seen sleeping on Sesha as they float along the cosmic ocean. It is believed that our universe exists in Vishnu's dream, and will end when Vishnu awakes from this dream.

According to legend, the great eagle Garuda stole Amrita, the elixer of immortality, out of heaven. Indra stole it back, but a few drops fell on to the grass below before he could return it. The serpents slithered on it, and hence snakes are able to shed their skins. Because of this ability to regenerate by shedding their skins, they are closely associated with Shiva, the god of regeneration from destruction.

You can often find depictions of nagas adorning temple walls and stairways. Since temple ceilings are made of wood and thus susceptible to fire, these gods of rain are often depicted lining the ornate roofs of temples.