Shankara is an enormously important figure in Hinduism, most particularly my branch of Advaita Vedanta. He was a brilliant philosopher from a young age and wrote amazing commentaries on all the Hindu scriptures in the 8th century CE.
He re-energized the branch of Hinduism known as Advaita or Smartha. He believed that the ultimate reality was one of complete unity.
During his young life, he traveled by foot over all of India discussing and spreading his ideas, attempting to unify Hinduism. It was a great revival and brought fresh interest in the ancient way of life. Buddhism and Jainism were getting more popular in that time and Shankara brought Hinduism back into people’s interests.
He is sometimes called also Shankaracharya (Shankara-Acharya), the “acharya” part meaning teacher. He founded four monasteries in the four cardinal directions within India and those monasteries are here today. When there is a teacher who is considered worthy of the role, one might be initiated as a Shankaracharya. The guru that my parents are devotees of, Sri Bharati Tirtha, is the Shankaracharya in the math in the south (located in Sringeri).
It is said that he died at 32, burning with brilliance for a short time and leaving a lasting impression on the world. He was a true sanyasin, living the life of a celibate monk and focusing all his energies on expounding Truth.
He denounced an obsessive focus on ritual and encouraged people to think for themselves and to look for God within.
His teachings can be summed up in this one phrase:
Brahma Satyam Jagat Mithya, Jeevo Brahmaiva Na Aparah
Brahman alone is real, this world is unreal; the Jiva is identical with Brahman.