Concept:The Mahad Satyagraha was a protest led by Dr. B. R. Ambedkar to assert the right of untouchables to use a public water tank in Mahad, Maharashtra.Explanation:On 20 March 1927, Dr. B. R. Ambedkar organized a satyagraha at the Chavdar Tale (public tank) in Mahad, a town in Konkan.The aim was to challenge the social ban that prevented Dalits (untouchables) from drawing water from the tank.Ambedkar chose Mahad because there was some support from caste Hindus there.This event is a landmark in the Dalit rights movement in India.The day is now observed as Social Empowerment Day in India.Answer:B. R. Ambedkar.