Manabendra Nath Roy (21 March 1887 – 26 January 1954), born Narendra Nath Bhattacharya, was an Indian revolutionary, radical activist and political theorist, as well as a noted philosopher in the 20th century.
Roy was a founder of the Mexican Communist Party and the Communist Party of India.
He was also a delegate to congresses of the Communist International and Russia's aide to China.
Following the rise of Joseph Stalin, Roy left the mainline communist movement to pursue an independent radical politics.
In 1940 Roy was instrumental in the formation of the Radical Democratic Party, an organisation in which he played a leading role for much of the decade of the 1940s.
In the aftermath of World War II Roy moved away from Marxism to espouse the philosophy of radical humanism, attempting to chart a third course between liberalism and communism.