Reverentially called Bhagavatpada Acharya (The teacher at the feet of Lord) and Adi Sankara (roughly "the first Sankara"), Sankara (approximately 788-820 CE) was the most famous Advaita philosopher who had a profound influence on the growth of Hinduism through his non-dualistic philosophy. He advocated the greatness and importance of the important Hindu scripture known as the Vedas (most particularly on the Upanishads, also known as Vedanta)and gave new life to Hinduism when it was suffering due to the increasing influence of Buddhism. He was born in Kaladi, a small village in Kerala, India. His teachers include Gaudapada and Govinda.
During Sankara's time Hinduism had lost some of its appeal, because of the influence of Buddhism. Sankara stressed the importance of the Vedas and his work helped Hinduism regain strength and popularity. Although he did not live long, he had traveled on foot to various parts of India to restore the study of the Vedas.
Sankara's theology maintains that spiritual ignorance (avidya) is caused by seeing the self (atman) where self is not. Discrimination needs to be developed in order to distinguish true from false and knowledge (jnana) from ignorance (avidya).
The philosophy that Shankara proposed was powerful and capitalized on years of dormant monist and mystic understandings of existence. He proposed that while the phenomenal universe, our consciousness and bodily being, are certainly experienced, they are not true reality. He did not mean to negate it, but considered that the ultimate truth was Brahman, the one divine ground that is beyond time, space and causation. Brahman is immanent and transcendant, but not merely a pantheistic concept. Indeed, while Brahman is the efficient and material cause for the cosmos, Brahman itself is not limited by its self-projection and indeed transcends all binary opposites/dualities, especially such individuated aspects as form and being, since it is incomprehensible by the human mind. We must pierce through a hazy perspectival lens to understand our true being and nature that is not perennial change and mortality but unmitigated bliss for eternity. If we are to understand the true motive force behind our actions and thoughts, we must become aware of the fundamental unity of being. How, he asks, can a limited mind comprehend the limitless Self? It cannot, he argues, and therefore we must transcend even the mind and become one with Soul-consciousness.
He denounced caste and meaningless ritual as foolish, and in his own charismatic manner, exhorted the true devotee to meditate on God's love and apprehend truth. His treatises on the Upanishads, Bhagavad Gita and Vedanta Sutras are testaments to a keen and intuitive mind that did not want to admit dogma but advocated reason. His greatest lesson was that reason and abstract philosophizing alone would not lead to moksha/liberation. It was only through selflessness and love governed by viveka (discrimination) that would see a devotee realize his inner Self. Charges that his philosophies were influenced by Buddhism are unfounded, since Shankara vehemently opposed negation of being (shunyata) and believed that the unmanifest Brahman manifested itself as Ishwara, the loving, perfect being on high who is seen by many as being Vishnu or Shiva or whatever their hearts dictate. Shankara is said to have traveled throughout India, from the south to Kashmir, preaching to the local populaces and debating philosophy (apparently successfully, though no documentation exists) with Buddhist scholars and monks along the way.
His impact on India and Hinduism cannot be stressed enough, as he countered the increasing sacerdotalism of the masses and reintroduced a purer form of Vedic thought. He presented a face of Hinduism that could reasonably contend with Buddhist ideas and spread it, as well as reformist measures, across the land, traveling from as far up as Kashmir from areas in the South of India.
Books written by Sankara for certain are:
The commentary Bhasya on the Brahma Sutra
The commentary on the Brhadaranyaka Upanishad
The commentary on the Taittiriya Upanishad
The Thousand Teachings or Upadesasahasri
A hymn to Krishna as the Herder of Cows, known as Bhaja Govindam
A hymn to the Goddess Saundaryalahari
Benedictory invocation to Siva and Sakti, namely Sivanandalahari
Books he probably wrote are:
The commentary on Gaudapada's Karika to the Mandukya Upanishad
The commentary on the Bhagavad Gita, though there is no scholarly agreement on this.
He is said to have founded four mathas (a matha is a monastery or religious order) which are important to this day. These are at Sringeri in Karnataka, in the south; Dwaraka in Gujarat in the west; Puri in Orissa in the east; and Jyotirmath (Joshimath) in Uttaranchal in the north. The heads of the mathas trace their authority back to him.
The matha at Kanchipuram or Kanchi in Tamil Nadu also claims its origin with him. According to legend this was where he himself settled in his last days. Some think the Kanchi matha lacks the legitimacy of the rest, but it is long-established and highly respected.