Indra was the supreme ruler of the gods in the early Hindu religious books, particularly the Rig Veda. Indra was the leader of the gods, the god of war, the god of thunder and storms, and the greatest warrior. He defended both gods and mankind against the forces of evil. His main celestial weapon is the Vajra, considered the lightening bolt (or a diamond).
In later times, Lord Indra slowly lost much of his grandeur, and eventually he became regarded as a god of the weather, or the king of lesser gods.