Hindu ascetic and social reformer who was the founder (1875) of the Arya Samaj, a Hindu reform movement advocating a return to the temporal and spiritual authority of the Vedas, the earliest scriptures of India.

Dayananda received the early education appropriate to a young Brahman of a well-to-do family. At the age of 14 he accompanied his father on an all-night vigil at a Śiva temple. While his father and some others fell asleep, mice, attracted by the offerings placed before the image of the deity, ran over the image, polluting it. The experience set off a profound revulsion in the young boy against what he considered to be senseless idol worship. His religious doubts were further intensified five years later by the death of a beloved uncle. In a search for a way to overcome the limits of mortality, he was directed first toward Yoga (a system of mental and physical disciplines). Faced with the prospect of a marriage being arranged for him, he left home and joined the Sarasvatī order of ascetics.

For the next 15 years (1845–60) he traveled throughout India in search of a religious truth and finally became a disciple of Swami Birajananda. His guru, in lieu of the usual teacher's fees, extracted a promise from Dayananda (the name taken by him at the time of his initiation as an ascetic) to spend his life working toward a reinstatement of the Vedic Hinduism that had existed in pre-Buddhist India.

Dayananda first attracted wide public attention for his views when he engaged in a public debate with orthodox Hindu scholars in Benares (Vārānasi) presided over by the maharaja of Benares. The first meeting establishing the Arya Samaj (Society of Aryans 【Nobles】) was held in Bombay on April 10, 1875. Although some of Dayananda's claims to the unassailable authority of the Vedas seem extravagant (for example, modern technological achievements such as the use of electricity he claimed to have found described in the Vedas), he furthered many important social reforms. He opposed child marriage, advocated the remarriage of widows, opened Vedic study to members of all castes, and founded many educational and charitable institutions. The Arya Samaj also contributed greatly to the reawakening of a spirit of Indian nationalism in pre-Independence days.

Dayananda died after vigorous public criticism of a princely ruler, under circumstances suggesting that he might have been poisoned by one of the maharaja's supporters; but the accusation was never proved in court.