Jesus Christ was this dude that was born like 2000 years ago. He was God incarnate. The whole trinity thing gives me a bit of a headache, but I'll try this on anyway. There's God, right? Then there's Jesus. Jesus is considered God's son. Jesus is also God. Then there's the Holy Spirit, which is also God. The Holy Spirit is the one who gives christians power beyond themselves. I'm sure there are websites that do a better job of explaining it, but that is my understanding.
Why did I say all that? Anticipation of the follow up, I guess. Yes, I know, God was his own Dad then God died and God resurrected himself. It's a mind screw, believe me.
Who was he? Average Jew dude, carpenter maybe, probably liked to fish.
Not all Christians have beleived that Jesus was God incarnate.
Not all Christians believe in the Trinity.