He is not from Earth, he is from Eridanus II. He was born in 2511. When he was a child he was taken from his family and put into the SPARTAN-II project.
He doesn't have one.
go to halopedia it's there
I'll always keep you safe
beat the game and he is not in it. master chiefs story happens about 20-30 year later
they want it to be mysterious like, "who is that guy" "what does he look like"