Short answers, pulled from the story.
Five hymns out of 1028 in the Rigveda are dedicated to Vishnu, yet this minor solar deity rose to become a supreme god. In Mandala 7 section 99 the text describes him as the one who separates heaven and earth with his strides.
The Mahabharata states that Vishnu will appear in ten specific incarnations to restore cosmic order. Lists vary across different Puranas such as the Agni Purana or Bhagavata Purana where some texts list twenty-two avatars while others mention only ten primary ones.
The Puranic period from 300 CE to 1200 CE saw the rise of synthetic Hinduism where Vishnu absorbed local traditions. The Bhagavata Purana emerged as the most popular text relating to the avatar Krishna during this era.
Tamil poet-saints known as Alvars traveled across India singing praises of Vishnu during the mid first millennium CE. Their poems compiled as Divya Prabhandham became an influential scripture for Vaishnavas and helped establish temple sites such as Srirangam.
Historic identifiers of Vishnu include his image holding a conch shell named Panchajanya and a war discus called Sudarshana. He is typically shown with four arms wearing yellow garments and a crown called Kiritamukuta.
Buddhists in Sri Lanka venerate Vishnu as the custodian deity of their island nation and protector of Buddhism. Chronicles like Mahavamsa state that Buddha himself handed over custodianship to Vishnu or delegated it to Sakra.