The Infinite Forms of Lord Vishnu
Lord Vishnu has assumed innumerable forms for the benefit of mankind. He is of infinite forms. Among these, the 10 Incarnations (Dasavatharam) such as Matsya, Kurma, etc., and the 24 sacred forms such as Kesava, Narayana, etc., are most familiar to devotees.
The Gayathri Mantra and Mahamantra describe these various forms of Lord Vishnu. Each letter in the Gayathri Mantra and Mahamantra represents one sacred form of the Lord.
Gayathri Mantra
Om Bhorba Vassuvaha, Tatsa Vithur Varenyam Bhargodevasya Deemahi Deyoyona Prasaddhayat
Maha Mantra
Om Namo Bhagavate Vasudevaya