The Life of the Great Shankaracharya

There are many questions behind the life of the Great Shankaracharya. He was and is said to have been a great Avatar. An avatar is a descent, a down-coming (from the verb tri, to cross over, attain, save, with the prefix ava, down; and so ava-tri descend into, appear, become incarnate). Can humans prove his existence as a divine incarnation, and if so how does it change human existence?
It has been said that Sankara was a divine incarnation of the Lord Siva and also the Lord Surya. Sivarahasya says: Thus, Lord Siva, the blue-necked one, will out of his boundless grace, undertake a num…