Lord Krishna is God (The Supreme Personality of Godhead). He has appeared more than 18,000 times in His original form as Krishna and millions of times in His other forms and each time He appears, many demonic living beings challenge Him. Lord Krishna very easily defeats them all. Also, every time He appears, He saves all His followers. This is simple proof that He is the one and only God. Do you know anyone else who has appeared millions of times and each time proved He was God? Do you know anyone else who has appeared more than once in their same body?
“I am the origin of the whole creation. Everything emanates from me. The wise worship me [Krishna] with devotion.”(Lord Krishna, Bhagavad-Gita 10.8)
There are millions of universes and Lord Krishna is the origin of everything.
“With a single particle of Myself [Krishna], I maintain the entire creation.”(Lord Krishna, Bhagavad-Gita 10.42)
With a tiny particle of Himself, Lord Krishna creates and maintains millions of universes. This is how great Lord Krishna (God) is. There are many who claim themselves to be God, or their followers claim them to be God. But how many of them actually prove themselves to be the God. Lord Krishna very clearly proved Himself to be the God, not just once but millions of times. Full details can be found in the Srimad-Bhagavatam.