In pre-Vedic times Mitra was probably far more important, but his prominence faded with time. In the Rig Veda, he is always presented with Varuna, who is said to be his twin, and like his brother he is one of the Adityas. This god fared far better in Persia under the name of Mithra, from whence his cult spread all the way to Rome where he was called Mithras.
Mitra is a Vedic god who stood for the sun, and was, with his brother Varuna, the guardian of the cosmic order. He was the god of friendships and contracts, and watched over the daytime hours. He was good-natured and on far better terms with humanity than was his brother. He is seen as a mediator between the gods and man.