As everyone knows, gods and demons have been constantly at war with each other. Demons hated the gods but even after every defeat in the battles that they fought, they would gather their army again and launch another attack on the gods.
Ahi, a demon, was so angry with the gods that he vowed to himself to wipe them out completely from all the three worlds. He tried to play a number of tricks on them to overpower them but failed in every battle that he fought. Ultimately he decided to change his form. He acquired the form of a huge serpent called Vritra and began to dry up all the oceans, one after another, by drinking up all the water. One day, when all the gods were busy attending a celestial sacrifice, Ahi swallowed all the cosmic water and coiled himself tightly around a mountain peak.
When the gods returned home and found not a drop of water to drink, they immediately realised that it was the doing of Vritra and no one else. They turned to Indra for help. Indra took out his white elephant Airavata and climbing upon it, he took a thunderbolt in one hand and arrows and a hook in another. He left to confront Vritra.
Indra travelled a long distance till he came to a mountain around which a giant serpent was coiled around. It immediately struck Indra that this could be no one else but Ahi who had coiled himself around the mountain. So he took aim and began shooting his arrows at the serpent. But none of the arrows hit the serpent. Instead the arrows got bent and dropped to the ground. Indra then threw the net around the mountain but that too could not dislodge the mountain or the serpent. Indra stopped for a few minutes to plan his next move. He decided to hit at the serpent’s face but the face was not visible. Ultimately his eyes fell on the fat stomach of the serpent and deciding that the bloated stomach was due to the water that the serpent had guzzled, Indra aimed his thunderbolt at the stomach of the serpent. The stomach burst open and water gushed out with huge force. Vritra was killed and water returned to all the oceans. From that day onwards, Indra is worshipped by everyone whenever a drought strikes anyone’s land.