Vishnu (Sanskrit: विष्णु) is a main Vedic God (including His different avataras and/or expansions), venerated as the Supreme Being in the Vaishnavism. He is also commonly known as Narayana or Hari. Smarta followers of Adi Shankara, among others, venerate Vishnu as one of Panchayatana puja. 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. This illustrates the omnipresent characteristic of Vishnu. Vishnu governs the aspect of preservation and sustenance of the universe, so he is called "Preserver of the universe".
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.
His eternal or permanent abode beyond the material universe is Vaikuntha which is a realm of eternal bliss and happiness. It is also known as Paramdhama, which means final or highest place for liberated souls, where they enjoy eternal bliss and happiness. Vaikuntha is situated beyond the material universe and hence, can not be perceived or measured by material science and logics.
His other abode within the material universe is Ksheera Sagara, where he reclines and rests on Shesha. It is known to be the topmost realm in the material universe, even higher than Satyaloka where Brahma resides. Vishnu manages and sustains the universe from there. Hence, Ksheera Sagara is also sometimes known as local Vaikuntha of the material universe, which is approachable by demigods in order to meet the lord in case of any emergency or disturbance in universal balance.
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. 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.
The Trimurti (English: ‘three forms’; Sanskrit: trimūrti) 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.