Vishnu is the Supreme god in the Vaishnavite tradition of Hinduism. Smarta followers of Adi Shankara, among others, venerate Vishnu as one of the five primary forms of God.

Vishnu Sahasranama

The Vishnu Sahasranama declares Vishnu as Paramatman (supreme soul) and Parameshwara (supreme God). It describes Vishnu as the All-Pervading essence of all beings, the master of — and beyond — the past, present and future, one who supports, sustains and governs the Universe and originates and develops all elements within. Vishnu governs the aspect of preservation and sustenance of the universe, so he is called 'Preserver of the universe'.

Puranas (includes Vishnu Puran)

In the Puranas, Vishnu is described as having the divine colour of water filled clouds, four-armed, holding a lotus, mace, shankha (conch) and chakra (wheel). Vishnu is also described in the Bhagavad Gita as having a 'Universal Form' (Vishvarupa) which is beyond the ordinary limits of human perception or imagination.

In almost all Hindu denominations, Vishnu is either worshipped directly or in the form of his ten avatara, most famous of whom are Rama and Krishna. The Puranabharti describes each of these Dasavatara of Vishnu. Among the ten principal Avatara described, nine have occurred in the past and one will take place in the future, at the end of Kali Yuga. In the commentary of creator Brahma in Vishnu Sahasranamam, he refers to Vishnu as "Sahasrakoti Yuga Dharine", which means that these incarnations take place in all Yugas in cosmic scales, the avatars and their stories show that god is indeed unimaginable, unthinkable and unbelievable. The Bhagavad Gita mentions their purpose as being to rejuvenate Dharma and vanquish negative forces, the forces of evil that threaten Dharma, as also to display His divine nature in front of the conditioned/fallen souls.

Trimurti

The Trimurti (English: ‘three forms’; Sanskrit: trimurti) is a concept in Hinduism "in which the cosmic functions of creation, maintenance, and destruction are personified by the forms of Brahma the creator, Vishnu the maintainer or preserver, and Shiva the destroyer or transformer." These three deities have been called "the Hindu triad" or the "Great Trinity". Of the three members of the Trimurti, the Bhagavata Purana, which espouses the Vaishnavite viewpoint, explains that the greatest benefit can be had from Vishnu.