Who He Is
Vishnu is the protector in the Trimurti — the three great forms of God. He is pictured resting peacefully on the giant serpent Adisesha, floating on the ocean of milk, with Goddess Lakshmi beside him. In his four hands he holds a conch (the sound of creation), a discus (the wheel of time that protects dharma), a lotus (purity), and a mace (strength). His rest is not sleep — it is calm watchfulness over the whole universe.
The Ten Avatars
The most loved teaching about Vishnu is his promise: whenever evil grows too strong, he will come down to earth to protect the good. These comings are called avatars. Tradition counts ten great ones — the Dashavatara: Matsya the fish, Kurma the turtle, Varaha the boar, Narasimha the half-lion, Vamana the small brahmin, Parashurama the warrior sage, Rama the perfect prince, Krishna the divine guide, Buddha the compassionate, and Kalki, who is yet to come. Rama and Krishna are so loved that they are worshipped in their own right across the world.
Festivals
Vishnu is worshipped in countless forms and festivals — Rama Navami for Rama, Janmashtami for Krishna, and Vaikuntha Ekadashi, when temple doors called 'Vaikuntha Dwaram' open and devotees pass through them seeking his blessing. The famous chant 'Om Namo Narayanaya' is his.