The supreme deva of Hinduism, during the early Vedic period, was Indra (इन्द्र) -- god of weather and war. The Rig-Veda states, "He under whose command are horses and cows and villages and all chariots, who gave birth to the sun and the dawn and led out the waters, he, my people, is Indra." (2.12)"
Indra's weapon (which he used to kill Vritra, with the help of other gods), is the thunderbolt (Vajra), though he also uses a bow, net and a hook. He rode a large, albino elephant called Airavata, whose four tusks resemble mountains. Indra is the leader of the Devas, and also one of the Ashta-Dikpalas, representing the east. Originally, he was probably a solar deity, riding a gold chariot across the sky. He brought water to Earth, and as such is sometimes worshipped as a god of fertility who can resurrect soldiers who die in battle. He is married to Indrani (whose father, Puloman, Indra killed), and is the father of Arjuna (by Kunti), Jayanta, Midhusa, Nilambara, Rbhus, Rsabha and Sitragupta. Indra is also the father of Vali and Surya. He is attended to by the Maruts (and the vasu), children of Diti and Rudra. Indra had murdered Diti's previous children, so she hoped her son would be more powerful than him and kept herself pregnant for a century, practicing magic to aid her fetal son. When Indra discovered this, he threw a thunderbolt at her and shattered the fetus into the Maruts, a group of less powerful storm gods.
He lives in Svarga in the clouds around Mt. Meru. Deceased warriors went to his hall after death, where they lived without sadness, pain or fear. They watched the Apsaras and the Gandharvas dance, and played games.
Vritra, an asura, stole all the water in the world and Indra drank much Soma to prepare himself for the battle with the huge serpent. He passed through Vritra's ninety-nine fortresses and then slew the monster. He brought water back to Earth.
In a later version of the story, Vritra was created by Tvashtri to get revenge for Indra's murder of his son, Trisiras. Vritra won the battle and swallowed Indra, but the other gods forced him to vomit Indra out. The battle continued and Indra fled. Vishnu and the rishis brokered a truce, and Indra swore he would not attack Vritra with anything made of metal, wood or stone, nor anything that was dry or wet, or during the day or the night. Indra used the foam from the waves of the ocean to kill him at twilight.
In later, Brahamanic times, Indra's position was stolen by Vishnu and Shiva. He needs their help to kill Vritra. According to the Mahabharata, a horrible goddess named Brahminicide came from the dead corpse of Vritra (herein a Brahman) and pursued Indra, who hid inside a lotus flower. Indra went to Brahma and begged forgiveness for having killed a Brahman.