Adi Shankara (traditionally 8th century CE) is the pre-eminent exponent of Advaita Vedanta, "non-dual" Vedanta, the most influential of the schools that interpret the Upanishads. Its central claim is a strict non-dualism: the ultimate reality, brahman, is one, without a second, and the innermost self, atman, is not merely similar to but identical with it, tat tvam asi, "that thou art." The world of multiplicity, and the individual's sense of being a separate self within it, is the work of maya, a beginningless cosmic ignorance (avidya) that misperceives the one reality as many.
Liberation (moksha) is therefore not an attainment of something new but the removal of ignorance, the direct realization that one's true self was always the undivided brahman. Shankara developed this through close commentary on the "triple canon" (prasthanatrayi): the principal Upanishads, the Bhagavad Gita, and the Brahma Sutras. He distinguished two levels of truth, the conventional and the absolute, allowing ordinary religious life its place while insisting on the higher, non-dual realization as final.