Who is Krishna?

Krishna is Sanskrit word for "the all-attractive Person." This name is used to refer to the supreme being in Vedic scriptures, especially those dealing with the science of devotion to God like the Srimad-Bhagavatam and the Bhagavad-gita. Bhagavad-Gita and Srimad-Bhagavatam explain that Krishna is the original supreme person, the Absolute Truth, the ultimate source of all energies and of all other incarnations of God.
Srimad-Bhagavatam describes about Krishna. As per Srimad-Bhagavatm Krishna is the Supreme Personality of Godhead. The Bhagavatam's first nine cantos describe Krishna as the almighty origin of all things, how He creates and maintains the universe, and some of His many avatars (incarnations), while the Tenth Canto gives us a picture of His private life — as a beautiful, playful young cowherd boy in the rural setting of Vrindavan.
In the Bhagavad-Gita , which Krishna spoke to His friend and devotee Arjuna on the battlefield of Kurukshetra some five thousands years ago, He explains about nature, soul, Karma, different types of yoga system and finally the importance of bhakti-yoga (devotional services).