Agni (Sk.). The God of Fire in the Veda; the oldest and the most revered of Gods in India. He is one of the three great deities: Agni, Vâyu and Sûrya, and also all the three, as he is the triple aspect of fire; in heaven as the Sun; in the atmosphere or air (Vâyu), as Lightning; on. earth, as ordinary Fire. Agni belonged to the earlier Vedic Trimûrti before Vishnu was given a place of honour and before Brahmâ and Siva were invented.
Source: H.P.Blavatsky - The Theosophical Glossary