Adi Shankara was the first philosopher who is believed to consolidate the doctrine of Advaita Vedanta, which is also regarded as a sub-school of Vedanta. He is also known as Shankara Bhagavatpadacharya and Adi Sankaracharya. All his teachings are based on the unity of the soul and Brahmin.

The dates of Shankara cannot be firmly established but some scholars date him between 788 and 820 CE. He certainly cannot have lived before the middle of the seventh century as he refers to the Mimamsaka theologian Kumarila and the Buddhist Dharmakirti who can be dated to that century. There are a number of traditional biographies, the Shankaravijayas, written by his followers. These texts agree that he was born in Kaladi, a small village in Kerala. His father died when he was young and he was brought up by his mother. Adi Shankara was named Shankara in the honor of Lord Shiva. The initiation of Shankara into student life was performed at the age of five. He mastered all the four Vedas at the age of eight. From a very young age Shankara was attracted to the monastic life. After his mother gave him permission to enter into the renunciatory stage, Adi Shankara traveled left Kerala and traveled to the northern part of India in search of a holy tutor. He then became the disciple of Bhagavatapada and wrote a commentary on Brahma Sutras and also propagated Advaita Vedanta. On his mission to propagate his philosophy he met a young man named Sanandana from Choladesha in South India who in the later ages became his first disciple. One of the most famous debates of Adi Shankara was with the ritualist Mandana Mishra.

As a young Nambudri Brahman boy of about eight, Shankara is said to have vowed to become a renouncer but his mother would not let him. Adi Shankara is regarded as the incarnation of Lord Shiva according to the Smarta Tradition. This great prophet toured the whole of India with the sole purpose of propagating his teachings through religious discourses and debates with other eminent philosophers and scholars. He is also the pioneer of four monasteries, which made a significant contribution to the historical development, revival, and spread of post-Buddhist Hinduism and essentials of Advaita Vedanta. He was also the founder of Dashanami monastic order and the Shanmata tradition of worship.

Shankara left home and found a guru, Govinda, by the Narmada river, whom he eventually left, then travelled north to Varanasi. Here he taught and gathered disciples. He went on a pilgrimage to the source of the Ganges and stayed at Badrinath for four years, where he composed his major works. He returned to Varanasi and continued to teach and debate with other thinkers, including the Mimamsaka Mandanamisra who converted to Advaita. Although many philosophical texts and devotional hymns are attributed to Shankara, the scholars of different traditions are agreed that `Shankara` is known especially as the author of the commentary on the Brahma Sutra. Apart from this text, three others are positively accepted as being of his authorship: the commentaries on the Brhadaranyaka and Taittiriya Upanisads and the independent work, the `Thousand Teachings` (Upadesasabari). He probably also wrote the commentary on Gaudapada`s Karika to the Mandukya Upanisad and the commentary on the Bhagavad Gita, though there is not universal agreement on this. Apart from the theological commentaries, Shankara is attributed by the Advaita and Sri Vidya traditions with the authorship of a famous hymn to the Goddess, the Saundaryalahari. His works are categorized under three heads namely `Bhasya` or commentary, `Prakarana Gratha` or philosophical treatise and `Stotra` or devotional hymn. The commentaries provided an unswerving elucidation of the scriptural texts; the philosophical treatises on the other hand provided various methodologies to the student to have a fair comprehension of the doctrine while the devotional hymns served to emphasize the relationship between the devotee and the deity.

In his commentaries Shankara developed a theology in which he tried to establish that spiritual ignorance (avidya) or illusion (maya) is caused by the superimposition (adhyasa) of what is not the self onto the self. All knowledge is distorted by superimposition or projection, which prevents us from seeing our true nature as the self`s (atman`s) pure subjectivity, ontologically identical with the absolute (brahman). In order to realize the truth of the identity of the self with the absolute, a person must develop discrimination. Discrimination allows for a person to distinguish the self from what is not the self, true being from objects, and knowledge (vidyayjnana) from ignorance (avidya).

Shankara`s enterprise is to show how his Advaita interpretation of sacred scriptures is correct. It is a method of reading the texts and so gaining knowledge of revelation`s truth: the process is one of hearing (sravana), thinking (manana) and reflecting or meditating. While the idea of mystical experience (anubhava), which has been stressed in recent times in the West, is important for Shankara as the goal to which revelation leads, he is primarily concerned with the correct interpretation of scripture and the refutation of what he regards as false views. According to Shankara, the knowledge sections are of greater importance, for liberation is the Veda`s central message, and only knowledge leads to liberation. No action can discriminate the self from what is not the self, only knowledge can achieve this, as silver is suddenly seen to be shell.

Adi Shankara was the founder of four mathas to guide the Hindu religion and to bring about a major reformation in the Indian spiritual life. Each of the chiefs of these four mathas acquires the title of Shankaracharya after the first Shankara. Hinduism had begun to decline at the time of Adi Shankara`s life because of the deep impacts of the two religions, Buddhism and Jainism. Some of the opponents of Adi Shankara blamed him of teaching the religion of Buddhism in the garb of Hinduism. But he along with the help of Madhva and Ramanuja became active participants in the revival of Hinduism. To deal with logically establishing the doctrine of Advaita Vedanta was the main objective of his works. In the process of teaching he gave a very high priority on the personal experience of the student.

Having said this, Shankara does make concessions to the idea of devotion (bhakti) to a personal Lord (Ishvara) as a lower level of knowledge. Brahman, in its timeless essence as identical with the self, is beyond all predicates and qualities (nirguna), but in its temporal mode as the Lord it has attributes (saguna), and so can be approached through devotion as an object of consciousness. To see the absolute as the Lord is to maintain a distinction between self and absolute, which is to retain a vestige of ignorance which must finally be transcended. If reality is one, all distinctions must be illusory.