Krishna repeatedly comes to this world in various forms to perform specific functions. Such avatars distinguish themselves by performing extraordinary feats. They are known by references to them in the Vedas, including Srimad-Bhagavatam, which recounts histories of several prominent incarnations from the beginning of creation.
According to the Bhagavata Purana, which is a sattvic purana, asserts that Krishna is "Bhagavan Himself," and subordinates to itself all other forms: Vishnu, Narayana,Purusha, Ishvara, Hari, Vasudeva, Janardana, etc. Krishna is often described and portrayed as an infant or young boy playing a flute as in the Bhagavata Purana or as a youthful prince giving direction and guidance as in the Bhagavad Gita.
Puranic sources mention Krishna's disappearance marks the end of Dvapara Yuga and the start of Kali Yuga (present age), which is dated to February 17/18, 3102 BCE