Lord Vishnu is the all-pervasive Lord who expands into everything. He is the maintainer of the universe and the complete cosmic creation. He is called Vishnu because He overcomes all. He represents sattva-guna, or the mode of goodness by which everything is sustained. He is also called Narayana, which means the shelter, resting place or ultimate goal of all living entities. It also means the one whose abode is the causal waters (Karana Ocean), and one who lives in the hearts of all living beings. It is this sattva nature which gives the living beings the tendency to grow toward a higher truth, the light, a more cohesive and intense reality. In this sense, Lord Vishnu is also called Hari, or one who removes the darkness of illusion.
There are 3 types of Vishnu :
1. Maha Vishnu
He is an expansion of Lord Krishna.
2. Garbhodaksayi Vishnu
He is an expansion of Maha Vishnu. He enters into the Universes created by Maha Vishnu.
3. Ksirodaksayi Vishnu
He is an expansion of Garbhodakshayi Vishnu. He enters into the heart of each and every living entity.