Indra (/ˈɪndrə/; Sanskrit: इन्द्र, IPA: [in̪d̪rɐ]) is the Hindu and Vedic god of heaven, weather, and war, considered the king of the devas and svarga in Hinduism and Vedism. He is the national god of the Vedic Aryans, and is associated with the sky, lightning, weather, thunder, storms, rains, river flows, and war.

Indra is the most frequently mentioned deity and the supreme God in the Rigveda. during the early Vedic Period, He was considered superior to all other gods, and was celebrated for his powers based on his status as a god of order, and as the one who killed the great evil, an asura named Vritra, who obstructed human prosperity and happiness. Indra destroys Vritra and his "deceiving forces", and thereby brings rain and sunshine as the saviour of mankind.

Indra's significance diminishes in the post-Vedic Indian literature, but he still plays an important role in various mythological events. He is depicted as a powerful hero.

According to the Vishnu Purana, Indra is the title borne by the king of the gods, which changes every Manvantara – a cyclic period of time in Hindu cosmology. Each Manvantara has its own Indra and the Indra of the current Manvantara is called Purandhara.

Indra is also depicted in Buddhist (Pali: Indā) and Jain mythologies. Indra rules over the much-sought Devas realm of rebirth within the Samsara doctrine of Buddhist traditions. However, like the post-Vedic Hindu texts, Indra is also a subject of ridicule and reduced to a figurehead status in Buddhist texts, shown as a god who suffers rebirth. In Jain traditions, unlike Buddhism and Hinduism, Indra is not the king of gods, but the king of superhumans residing in Svarga-Loka, and very much a part of Jain rebirth cosmology. He is also the one who appears with his consort Indrani to celebrate the auspicious moments in the life of a Jain Tirthankara, an iconography that suggests the king and queen of superhumans residing in Svarga reverentially marking the spiritual journey of a Jain. He is a rough equivalent to Zeus in Greek mythology, or Jupiter in Roman mythology. Indra's powers are similar to other Indo-European deities such as Norse Odin, Perun, Perkūnas, Zalmoxis, Taranis, and Thor, part of the greater Proto-Indo-European mythology.

Indra's iconography shows him wielding his vajra and riding his vahana, Airavata. Indra's abode is in the capital city of Svarga, Amaravati, though he is also associated with Mount Meru (also called Sumeru).

The etymological roots of Indra are unclear, and it has been a contested topic among scholars since the 19th-century, one with many proposals. The significant proposals have been:

Colonial era scholarship proposed that Indra shares etymological roots with Avestan Andra, Old High German *antra ("giant"), or Old Church Slavonic jedru ("strong"), but Max Muller critiqued these proposals as untenable. Later scholarship has linked Vedic Indra to Aynar (the Great One) of Circassian, Abaza and Ubykh mythology, and Innara of Hittite mythology. Colarusso suggests a Pontic origin and that both the phonology and the context of Indra in Indian religions is best explained from Indo-Aryan roots and a Circassian etymology (i.e. *inra). Modern scholarship suggests the name originated at the Bactria–Margiana Archaeological Complex where the Aryans lived before settling in India.