In ancient Hinduism (early Vedic Period), the Vritra was a horrible sea dragon known to cause death and drought to the people. He would block the flow of the river, allowing the people on land to die without access to precious water.
The god of rain and thunderstorms, Indra, had to come down and whoop Vritra's arse. He started by destroying all 99 of Vritra's palaces with his fashioned thunderbolt (sound familiar). The battle was a violent one. Vritra broke Indra's jaw, in fact, before being defeated.
Vritra's mother was also killed by Indra.
Later, Vritra's myth was altered during the Puranic Period. Here, Vritra is a demon who swalows Indra. But the other gods force Vritra to vomit him out.
I know. Weird. It get's even weirder.
Vishnu promises not to attack Vritra with metal, wood, or stone. So Indra uses the ocean foam to somehow kill Vritra. Not sure how that works, but he did it.
Yea Indra! Boo Vritra!