In comparing historically Varuṇa and Indra, whose importance was about equal in the earlier period of the Rigveda, it seems clear that Varuṇa was greater in the Indo-Iranian period, but became inferior to Indra in later Vedic times. Indra, on the other hand, became in the Brāhmaṇas and Epics the chief of the Indian heaven, and even maintained this position under the Puranic triad, Brahmā-Vishṇu-Çiva, though of course subordinate to them.
At least three of the lesser deities of the air are connected with lightning. One of these is the somewhat obscure god Trita, who is only mentioned in detached verses of the Rigveda. The name appears to designate the "third" (Greek, trito-s), as the lightning form of fire. His frequent epithet, Āptya, seems to mean the "watery." This god goes back to the Indo-Iranian period, as both his name and his epithet are found in the Avesta. But he was gradually ousted by Indra as being originally almost identical in character with the latter. Another deity of rare occurrence in the Rigveda, and also dating from the Indo-Iranian period, is Apāṃ napāt, the "Son of Waters." He is described as clothed in lightning and shining without fuel in the waters. There can, therefore, be little doubt that he represents fire as produced from the rain-clouds in the form of lightning. Mātariçvan, seldom mentioned in the Rigveda, is a divine being described as having, like the Greek Prometheus, brought down the hidden fire from heaven to earth. He most probably represents the personification of a celestial form of Agni, god of fire, with whom he is in some passages actually identified. In the later Vedas, the Brāhmaṇas, and the subsequent literature, the name has become simply a designation of wind.
