Shiva (; Sanskrit: शिव, romanized: Śiva, lit. 'The Auspicious One' [ɕɪʋɐ]), also known as Mahadeva (; Sanskrit: महादेव:, romanized: Mahādevaḥ, lit. 'The Great God' [mɐɦaːd̪eːʋɐ]), or Hara, is one of the principal deities of Hinduism. He is the Supreme Being in Shaivism, one of the major traditions within Hinduism.

Shiva is known as "The Destroyer" within the Trimurti, the Hindu trinity which also includes Brahma and Vishnu. In the Shaivite tradition, Shiva is the Supreme Lord who creates, protects and transforms the universe. In the goddess-oriented Shakta tradition, the Supreme Goddess (Devi) is regarded as the energy and creative power (Shakti) and the equal complementary partner of Shiva. Shiva is one of the five equivalent deities in Panchayatana puja of the Smarta tradition of Hinduism.

Shiva has many aspects, benevolent as well as fearsome. In benevolent aspects, he is depicted as an omniscient Yogi who lives an ascetic life on Mount Kailash as well as a householder with his wife Parvati and his three children, Ganesha, Kartikeya and Ashokasundari. In his fierce aspects, he is often depicted slaying demons. Shiva is also known as Adiyogi (the first Yogi), regarded as the patron god of yoga, meditation and the arts.

The iconographical attributes of Shiva are the serpent Vasuki around his neck, the adorning crescent moon, the holy river Ganga flowing from his matted hair, the third eye on his forehead (the eye that turns everything in front of it into ashes when opened), the trishula or trident as his weapon, and the damaru drum. He is usually worshipped in the aniconic form of lingam.

Shiva has pre-Vedic roots, and the figure of Shiva evolved as an amalgamation of various older non-Vedic and Vedic deities, including the Rigvedic storm god Rudra who may also have non-Vedic origins, into a single major deity. Shiva is a pan-Hindu deity, revered widely by Hindus in India, Nepal, Sri Lanka and Indonesia (especially in Java and Bali).