Thirumarugal Natesapillai Rajarathinam Pillai (27 August 1898- 12 December 1956) or TNR was an Indian Carnatic musician, nadaswaram maestro, vocalist and film actor. He was popularly known as "Nadaswara Chakravarthi" (literally, the Emperor of Nadaswaram).

Rajarathinam Pillai was born Balasubramanian to his parents, Kuppuswami Pillai and Govindammal at Thiruvaduthurai in Thanjavur District in South India. His father was an exponent of Carnatic music. He was given in adoption to his uncle Thirumarugal Natesa Pillai, who was his guru initially and a nagaswaram player who was regarded as an exponent of raga improvisation/ elaboration, and took his initials and the name Rajarathnam from then on.

Rajarathnam Pillai married five times and died without issues. Contrary to the prevailing norms of dress for nadaswaram players, who, as temple servants, would dress humbly, Pillai often appeared in concerts wearing shirt and trousers or, on occasions, wore the dress favored by the Hindustani musicians.