Vishnu is a Hindugod. He is the second god of the Trimurti (also called the Hindu Trinity), along with Brahma and Shiva. Known as the Preserver, he is most famously identified with his avatars, most especially Krishna and Rama.
Vishnu's consort is Lakshmi, the Goddess of wealth. Shakti is the samvit [the primary intelligence] of god, while the other five attributes emerge from this samvid and hence Shakti is the god's ahamata [personality and activity. ] Thus this Shakti of god is personified in mythological lore and is called Shri or Lakshmi, and She is said to manifest herself in, 1] kriyäshakti, [Creative Activity] and 2] bhütishakti [Creation] of god. Hence Vishnu can not part with His own personality or creativity i.e., ahamta, which in its feminine form is called Sri or Lakshmi. He therefore needs consort Goddess Lakshmi to be with Him always, untouched by any. Thus goddess Lakshmi has to accompany Vishnu in all His incarnations.
His mount is Garuda, the eagle. He, along with the rishis, helped broker the truce between Vritra and Indra.
It is believed that he manifested himself as a human being in ten Avatars. He is frequently worshipped in the form of these avatars.
It is not clearly known when or how the worship of Vishnu began. In the Vedas, and the information on Aryan beliefs, Vishnu is listed as a lesser god, strongly associated with Indra. It was only later in Hindu history that he became a member of the Trimurti and one of the most important deities of the religion.