Adi Shankaracharya (8th century CE) was the primary philosopher and expounder of Advaita Vedanta, a non-dualistic school of Hindu philosophy. He wrote commentaries on the Upanishads, Bhagavad Gita, and Brahma Sutras. Ramanuja advocated for Vishishtadvaita, Madhavacharya for Dvaita, and Swami Vivekananda was a later proponent of Vedanta.