Sage Samvarta was an Avadhuta and his story is mentioned in
the Ashvamedha Parva of the Mahabharata. Sage Samvarta was the brother of
Brihaspati. One the advice of Narada, King Marutta (in some texts the name of the
king is Nivritta) invited Sage Samvarta to perform an important yajna.
Indra felt threatened by the Yajna and took the help of
Brihaspati. Brihaspati had thus declined to conduct the yajna. This is when
the king on the advice of Narada made Sage Samvarta the priest.
Brihaspati felt slighted at this and out of envy decided to
stop the Yajna.
To achieve success in his mission, Brihaspati took the help
of Indra, the king of Devas.
Indra deputed Agni to stop the yajna. Agni burned some tree
and creepers but could not face Sage Samvarta. The sage warned Agni that he
will be turned into ashes by the power of his life as a true Brahmachari. Agni
quickly returned to Indra and narrated about the powers of Samvarta.
Indra then deputed a Gandharva but he too was no match to
the yogic powers of Samvarta.
Finally Indra came to fight with Samvarta but realizing the
true power of a Brahmachari, he became friend of the sage helped him in completing
the Yajna. (Another version has it that Indra who created rain, thunder and
storm was cursed by the sage to become impotent).