Varuna was a very important god in early Vedic Indian religion. Though only about a dozen hymns address him in the Rig Veda, he had a position of stature among the deities. He was viewed as a lord of the cosmos, keeper of divine order and bringer of rain. He was also believed to be the enforcer of contracts, and was omnipotent.
Varuna is seen as a white man in golden armor riding a Makara (a sea monster), holding a noose or lasso made from a snake. He was worshiped with veneration and a healthy amount of fear, for as an Asura Varuna did have his sinister aspects and was known to punish mortals who did not keep their word.
He was the cosmic hangman and his usual method of punishment was to capture the offender with his noose. He was also a lord of the dead, a position he shared with Yama, and could confer immortality if he so chose.
In late Vedic times, the worship of Varuna fell off and Indra replaced him as king of the gods. Varuna became god of the oceans and rivers, which was still quite important. The souls of those who drowned went to him, and he was attended by the Nagas. Eventually Varuna faded away with the ascendancy of Shiva and Vishnu.