Indra (; Sanskrit: इन्द्र) is the king of the devas (god-like deities) and Svarga (heaven) in Hinduism. He is associated with the sky, lightning, weather, thunder, storms, rains, river flows, and war. Indra's powers are similar to other Indo-European deities such as Jupiter, Perun, Perkūnas, Zalmoxis, Taranis, Zeus, and Thor, part of the greater Proto-Indo-European mythology.

Indra is the most referred deity in the Rigveda. He is celebrated for his powers, and as the one who killed the great evil (a malevolent type of asura) named Vritra, who obstructed human prosperity and happiness. Indra destroys Vritra and his "deceiving forces", and thereby brings rains and sunshine as the saviour of mankind. He is also an important deity worshipped by the Kalash people, indicating his prominence in ancient Hinduism.

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, and is known for having sexual relations with sage Gautama's wife, Ahalyā.

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 (Indā in Pali) 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 that 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 wife 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 (heaven) reverentially marking the spiritual journey of a Jain.

Indra's iconography shows him wielding a lightning thunderbolt weapon known as Vajra, riding on a white elephant known as Airavata. In Buddhist iconography, the elephant sometimes features three heads, while Jain icons sometimes show the elephant with five heads. Sometimes, a single elephant is shown with four symbolic tusks. Indra's abode exists in the capital city of Svarga, Amaravati, though he is also associated with Mount Meru (also called Sumeru).