The word 'Krishna' derived from Sanskrit has been interpreted differently by people over the ages. The most literal derivation is 'all-attractive'.
Lord Krishna is the whole existence in itself - Krishna includes everything. As is often seen in the pictures or stories of Lord Krishna, everything is attracted to him...be it the cows, birds, trees, cowherds, the water of Vrindavana, Gopis, Pandavas, or anyone who has come to meet or know Him.
According to Parasara Muni, a Rigvedic Maharishi and author of many ancient Indian texts, only the one who possesses strength, fame, wealth, knowledge, beauty and renunciation -all the six opulence- at the same time and to an unlimited degree, can be deemed as the Supreme Personality of Godhead.
During his lifetime on earth, Krishna has through his numerous actions proven that He possesses all the six opulence, in supreme capacity.