Adi Shankara (Sanskrit: आदिशङ्करः Ādi Śaṅkara, pronounced [aːd̪i ɕəŋkəɾə]) (788 CE - 820 CE), also known as Śaṅkara Bhagavatpādācārya and Ādi Śaṅkarācārya was an Indian sage from Kalady in present day Kerala who consolidated the doctrine of advaita vedānta. His teachings are based on the unity of the ātman and brahman— non-dual brahman, in which brahman is viewed as nirguna brahman, brahman without attributes.

Shankara travelled across the Indian subcontinent to propagate his philosophy through discourses and debates with other thinkers. He is reputed to have founded four mathas ("monasteries"), which helped in the historical development, revival and spread of Advaita Vedanta of which he is known as the greatest revivalist. Adi Shankara is believed to be the organizer of the Dashanami monastic order and the founder of the Shanmata tradition of worship.

His works in Sanskrit concern themselves with establishing the doctrine of advaita (nondualism). He also established the importance of monastic life as sanctioned in the Upanishads and Brahma Sutra, in a time when the Mimamsa school established strict ritualism and ridiculed monasticism. Shankara represented his works as elaborating on ideas found in the Upanishads, and he wrote copious commentaries on the Vedic canon (Brahma Sutra, principal upanishads and Bhagavad Gita) in support of his thesis. The main opponent in his work is the Mimamsa school of thought, though he also offers arguments against the views of some other schools like Samkhya and certain schools of Buddhism.

Eknath Easwaran (December 17, 1910 – October 26, 1999) was a spiritual teacher, an author of books on meditation and ways to lead a fulfilling life, as well as a translator and interpreter of Indian literature.

In 1961 Easwaran founded the Blue Mountain Center of Meditation and Nilgiri Press, based in northern California. Nilgiri Press publishes over two dozen books he authored.

Eknath Easwaran was influenced by Gandhi, whom Easwaran met when he was a young man. Easwaran developed a method of meditation – silent repetition in the mind of memorized inspirational passages from the world's great religions – which later came to be known as Passage Meditation.

Eknath Easwaran was born in 1910 in a village in Kerala, British India.Eknath is his surname, Easwaran his given name. Brought up by his mother, and by his maternal grandmother whom he honored as his spiritual teacher, he was schooled in his native village until the age of sixteen, when he went to attend a Catholic college fifty miles away. Here he acquired a deep appreciation of the Christian tradition. He graduated at the University of Nagpur in English and law. He served as Professor of English literature at the University of Nagpur.