Adi Shankaracharya (c. 8th century CE), the great philosopher and theologian, revived and established Sanatana Dharma through his Advaita Vedanta philosophy. He composed profound commentaries on the Upanishads, Bhagavad Gita, and Brahma Sutras. To preserve and propagate Vedic knowledge, he founded four major mathas (monasteries) in the four corners of India: Sringeri, Dwaraka, Puri, and Badrinath. His scholarly and organisational efforts unified Hindu thought and strengthened the spiritual and cultural fabric of India.