The Vishnu Sahasranama describes Vishnu as the All-Pervading essence of all beings, the master of and beyond the past, present and future, the creator and destroyer of all existences, one who supports, sustains and governs the Universe and originates and develops all elements within.
In the Puranas, Vishnu is described as being the color of clouds (dark-blue), four-armed, holding a lotus, mace, 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 sense perception .
It is also within the Puranas that the information regarding Vishnu's avatars is given. Nine of these avatars, or 'incarnations' are described as having occurred in the past, with one still to happen at the end of Kali Yuga. The Bhagavad Gita mentions their purpose as being to rejuvenate Dharma and vanquish negative forces. In virtually all the Sanatana Dharma traditions, Vishnu is worshipped, either directly or through avatars such as Rama, Krishna, Varaha and Narasimha.
In the Trimurti, Vishnu is responsible for the maintenance or 'preservation' of the Universe, with the other roles of creation and destruction being under the care of Brahma and Shiva, respectively.