Story of Vishvarupa, who became the guru of Devas, and who was eventually killed by Indra, the king of Devas.
The story begins with Indra offending Brihaspati, the Guru of Devas. An angry Brihaspati disappeared from the universe. Without a guru the fortune of Devas waned, they lost battles and there was misfortune all around.
Devas led by Indra approached Brahma to find a solution.
Brahma scolded Indra for his arrogance of ignoring Brihaspati and warned him that without a Guru no king can survive.
Brahma advised Indra to approach Vishvarupa, son of Tvashta, and ask him to be the Guru of Devas. Vishvarupa was well versed in Vedas and what made him special was that he had three heads. He could thus recite the Rig Veda, Sama Veda and Yajur Veda alone.
Devas approached Vishvarupa with gifts and in reverence asked him to take the position of the Guru of Devas.
Vishvarupa readily accepted the invitation to become Guru of Devas.
To impress Indra, Vishvarupa presented him with Shiva Kavacham, a powerful shield.
Rachna, mother of Vishvarupa, was an asura. He had deep affection for his mother and this made him a supporter of asuras, the enemies of Devas. He had accepted the mantle of Guru to actually weaken the Devas.
At every yagna, he poured ghee into sacrificial fire saying aloud for the benefit of Devas. But in his mind he prayed for the sacrifice to benefit the Asuras.
Indra soon realized that after the arrival of the new Guru, the asuras were gaining in strength and the Devas were becoming weaker and weaker.
Soon, Indra found out about the treachery of Visvarupa. He rushed into the ashram of Vivarupa and beheaded the Guru.