Those who played games from the Half-Life series may remember a blue-suited (maybe purple) guy who was always around somewhere as if he were observing you. At the end of each episode / sequel the main character, Gordon Freeman, had some interaction with him.
The question is simple: Who is this guy?
I haven’t seen a clear explanation of this.
There is not a clear explanation of this. There’s not really even a good solid HINT of this. This is entirely deliberate on the part of the game developers – they haven’t revealed SQUAT about this guy.
The Nihilanth was of the opinion he wasn’t human, though: “You are man. He is not man.”
There’s a pretty good summary of everything we have at the Half-Life Wikia but I doubt you’ll learn anything you didn’t from playing the games (except possibly locations he shows up that you missed him).