Adi Sankara was an influential Indian philosopher and theologian who lived in the early 8th century. He is best known for consolidating the doctrine of Advaita Vedanta, which emphasizes non-dualism and the idea that the individual self (Atman) and the ultimate reality (Brahman) are one. His teachings and writings have had a profound impact on Eastern philosophy, shaping the understanding of spirituality and the nature of reality in Hindu thought.