Vishnu, also known as Narayana, is the Supreme Being or Ultimate Reality for Vaishnavas and a manifestation of Brahman in the Advaita or Smarta traditions of Hinduism. The Vishnu Sahasranama describes Vishnu as the All-Pervading essence of all beings, 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.
The traditional Sanskrit explanation of the name Vishnu involves the root "vis", meaning "to settle, to enter", or also (in the Rigveda) "to pervade", and a suffix "nu", translating to approximately "the All-Pervading One". An early commentator on the Vedas, Yaska, in his Nirukta, defines Vishnu as "vishnu vishateh; one who enters everywhere", and "yad vishito bhavati tad vishnurbhavati; that which is free from fetters and bondages is Vishnu."
In the Rigveda, Vishnu is mentioned 93 times. He is frequently invoked alongside other deities, especially Indra, whom he assists in killing Vritra, and with whom he drinks Soma. His companionship with Indra is still reflected by his later titles Indranuja and Upendra, both referring to Vishnu as being the brother of Indra. His distinguishing characteristic in the Vedas is his association with light and his identification with the Sun.
The most celebrated act of Vishnu in the Rigveda is the "three steps" by which he strode over this universe and in three places planted his step. The "Vishnu Sukta" of the Rig Veda says that the first and second of Vishnu's strides (those encompassing the earth and air) are visible to men and the third is in the heights of heaven (sky). This last place is described as Vishnu's supreme abode.