Short answers, pulled from the story.
Vishnu, also known as Narayana and Hari, is one of the principal deities of Hinduism and the Supreme Being within the Vaishnavism tradition. He is the god of preservation, associated with the quality of sattva, and holds the role of the Preserver within the Trimurti alongside Brahma and Shiva.
The ten primary avatars of Vishnu are collectively called the Dashavatara. They are the Fish (Matsya), the Tortoise (Kurma), the Boar (Varaha), the Man-Lion (Narasimha), the Dwarf (Vamana), Parasurama, Rama, Krishna, Buddha, and the future avatar Kalki.
Vishnu holds four objects: the conch shell Panchajanya, whose spiral form represents all interconnected cyclic existence; the war discus Sudarshana, symbolizing the restoration of dharma by force when evil overwhelms cosmic order; the club Kaumodaki, symbolizing authority and the power of knowledge; and a lotus flower, symbolizing purity and transcendence.
Vishnu appears in just five of the 1028 hymns of the Rigveda, placing him below major deities like Indra and Agni in textual frequency. His distinguishing characteristic in those early hymns is his association with light, and he is linked to Surya, the sun god. Scholar Jan Gonda argued he was likely more important among the general population than his hymn count suggests.
The Trivikrama refers to the three strides of Vishnu, described in several Rigvedic hymns. Beginning as a small, insignificant being, Vishnu expands and covers the earth with his first step, the ether with his second, and all of heaven with his third. The Vishnu Sukta 1.154 of the Rigveda states that the first two strides are visible to mortals and the third belongs to the realm of the immortals.
Vishnu is venerated across a wide geographic range beyond India. In Sri Lanka, Theravada Buddhists honor him as the custodian deity and protector of Buddhism. Vishnu statues dated to the 4th-9th century have been found in Thailand, Vietnam, and Cambodia. In Indonesia he is central to the wayang puppet tradition, and in 13th-century Japan he appears in Buddhist texts as Bichu-ten.