The correct answer is Ishwar Chandra Vidyasagar. Born in 1820 in Bengal, he was a Sanskrit scholar, educator, writer, printer and social reformer who became one of the central figures of the Bengal Renaissance. He lived by the principle of simple living and high thinking, and dedicated much of his life to social reform, especially the cause of widow remarriage, which was banned by orthodox Hindu custom at the time.
His campaigning led directly to the passing of the Hindu Widows' Remarriage Act on 26th July 1856, which legalized the remarriage of widows across British India, a landmark reform against deep rooted social restrictions. He was also instrumental in modernizing the Bengali alphabet and prose style, and he worked extensively on promoting women's education.
Raja Ram Mohan Roy, though also a major Bengal Renaissance reformer, is best known for his campaign against Sati and founding the Brahmo Samaj, and he had died in 1833, before the 1856 widow remarriage act was passed. Rabindranath Tagore was a poet and Nobel laureate born later, in 1861, not connected to this particular 1856 reform. Bankim Chandra Chatterjee was a novelist known for Vande Mataram and Anandamath, not the driving force behind this law. Only Vidyasagar fits every detail given.