Okay...
[crap]
His name is John-117 and he's part of a group of 75 who were selected as six-year-olds for their genetic makeup, kidnapped from their families, genetically and cybernetically enhanced, and trained by Chief Petty Officer Mendez, the best drill instructor in the UNSC armed forces.
The whole "Master Chief" thing is John's rank: Master Chief Petty Officer. He's the leader of the bunch, with his #2, Fred-104, being a Senior Chief Petty Officer.
And no, the SPARTAN IIs do not have social lives. The closest thing John-117 has to a friend is his tactical assistant, the AI named Cortana.
[/crap]
(Apologies to all my fellow Marathoners)