Erode Venkatappa Ramasamy (17 September 1879 – 24 December 1973), commonly known as Periyar, was an Indian social activist and politician. He was the organiser of the Self-Respect Movement and Dravidar Kazhagam and is considered the architect of Dravidian politics, as well as a leading figure of left-wing politics in India.

Periyar joined the Indian National Congress in 1919 and participated in the Vaikom Satyagraha, during which he was imprisoned twice. He resigned from the Congress in 1925, believing that they only served the interests of Brahmins. From 1929 to 1932, he toured British Malaya, Europe and the Soviet Union which later influenced his Self-Respect Movement in favour of caste equality. In 1939, he became the head of the Justice Party, which he transformed into a social organisation named Dravidar Kazhagam in 1944. The party later split, with one group led by C. N. Annadurai forming the Dravida Munnetra Kazhagam (DMK) in 1949. While continuing the Self-Respect Movement, he advocated for an independent Dravida Nadu (land of the Dravidians).

Periyar promoted the principles of rationalism, self-respect, women's rights and eradication of caste. He opposed the exploitation and marginalisation of the non-Brahmin Dravidian people of South India and the imposition of what he considered Indo-Aryan India. Since 2021, the Indian state of Tamil Nadu celebrates his birth anniversary as 'Social Justice Day'.

Erode Venkata Ramasamy was born on 17 September 1879 to a Kannada speaking Balija merchant family in Erode, then a part of the Coimbatore district of the Madras Presidency. Ramasamy's father was Venkatappa Nayakar (or Venkata), and his mother was Chinnathyee Muthammal. He had one elder brother named Krishnaswamy and two sisters named Kannamma and Ponnuthoy. He later came to be known as "Periyar", meaning 'respected one' or 'elder' in Tamil.

Periyar married when he was 19, and had a daughter who lived for only 5 months. His first wife, Nagammai, died in 1933. Periyar married for a second time in July 1948. His second wife, Maniammai, continued Periyar's social work after his death in 1973, and his ideas then were advocated by Dravidar Kazhagam.

In 1929, Periyar announced the deletion of his caste title Naicker from his name at the First Provincial Self-Respect Conference of Chengalpattu. He could speak three Dravidian languages: Kannada, Telugu and Tamil. Periyar attended school for five years after which he joined his father's trade at the age of 12. He used to listen to Tamil Vaishnavite gurus who gave discourses in his house enjoying his father's hospitality. At a young age, he began questioning the apparent contradictions in the Hindu mythological stories. As Periyar grew, he felt that people used religion only as a mask to deceive innocent people and therefore took it as one of his duties in life to warn people against superstitions and priests.

In 1904, Periyar went on a pilgrimage to Kashi to visit the revered Shiva temple of Kashi Vishwanath. Though regarded as one of the holiest sites of Hinduism, he witnessed immoral activities such as begging and floating dead bodies. His frustrations extended to functional Hinduism in general, when he experienced what he called "Brahmanic exploitation".

However, one particular alleged incident in Kasi had a profound impact on Periyar's ideology and future work. At the worship site, there were free meals offered to guests. To Periyar's shock, he was refused meals at choultries, which exclusively fed Brahmins. Due to extreme hunger, Periyar felt compelled to enter one of the eateries disguised as a Brahmin with a sacred thread on his bare chest, but was betrayed by his moustache. The gatekeeper at the temple concluded that Periyar was not a Brahmin, as Brahmins were not permitted by the Hindu shastras to have moustaches. He not only prevented Periyar's entry but also pushed him rudely into the street.