Advaita Acarya is God Himself, but still He plays the role of God's servant. Lord Caitanya comes and He brings Advaita Acarya and Nityananda Prabhu with Him to show that the position of a real servant of God is more glorified in the eyes of God Himself than His own position. Lord Caitanya is always surrounded by His devotees and He does not like to be glorified alone also, He is more pleased when we glorify His associates. In this age one person can not do anything alone, therefore the society of devotees is very important.
Advaita Acarya is a very particular incarnation of Lord Mahavisnu in His capacity of presiding deity of maya. There are two causes for this material creation: 1) nimita-karana or instrumental cause; 2) upadana-karana or material cause. And Lord Himself is nimita-karana and upadana-karana. The energy of nimita-karana is jivamaya or the living entities. When the Lord Himself becomes upadana-karana of this world, then His energy is maya or matter. Advaita Acarya is the manifestation of this upadana-karana.
Advaita Acarya lived 125 years. At the age of 25 he went on pilgrimage and visited all the holy places in India. His last destination was Vrindavan. While he was in Nandagram the Lord Himself appeared to him as a deity of Madana Gopal. After some time Advaita Acarya decided to go to Navadvip, because Lord Caitanya should appear there soon. But Madana Gopal wanted to stay in Vrindavan, so He told Advaita Acarya to find a painting of Him in Nidhivan, which was made by Visakha for Srimati Radharani. In Navadvip Advaita Acarya became a very famous professor with many followers, he established two schools. He had two houses in Shantipur and in Navadvip, and got married with two wives. At that time nobody was interested in bhakti. He preached "Bhagavad-gita" and "Srimad-Bhagavatam", but nobody was interested. Therefore he began to worship salagrama sila for God to come. He is acarya because he wants people to be happy, and therefore he is teaching how to become happy.