Sri Shankracharya

Adi shankaracharya with his disciples

Lord Shiva appeared as Sri Shankracharya.

He re-established the supreme authenticity and decorum of the Vedas, and founded the philosophy of ‘brahmakaran-vad’ (Brahm as Ultimate cause).

In later ages, the Vaishnav stalwarts built the philosophy of bhakti upon this same foundation stone.
Source: Dasavatar by Srila Bhakti Ballabh Tirtha Goswami Maharaj