This post is a work in progress...
Let's discuss Sean Walker for a moment. What do we know about him? Beyond that, who is he? Let's speculate!!!
We know he's got mad skillz. He's a computer whiz kid, an MIT graduate. He's also a great improviser. He also appears to be quite fast. Perhaps he's not super-humanly fast, but fast nonetheless.
In episode 1 ("I Haven't Told You Everything"), Michael Buchanan gives Sean his blessing to marry Leila. You could argue that he's gotten to know Sean over the past five years that Sean and Leila have been together, but perhaps it's more than that.
In episode 2 ("To Keep Us Safe"), Sean is recovered in the desert. He is severely dehydrated, after what sounds like a long time out there. That would kill most people, yet Sean recovers, and quite quickly. Michael Buchanan says, "only YOU can find her!" Now, WHY is that true? After 16 episodes (at the time of this writing), that seems to have more potential meaning than I thought at first.
In episode 4 ("A Matter of Life and Death"), in a flashback to Sean and Leila's first Thanksgiving together, Sean tells Leila, Michael and (mother) Buchanan that his parents split up when he was young. According to The Event's official wiki, "Sean notes that he has not really spoken with his parents since he left high school--that his parents split when he was a kid, that his mother was not well, and his father fell apart and began drinking after the separation." Now, this appears to be an innocuous comment, that he comes from a broken home, but perhaps it's more. At the time, we don't know of Michael's true life that we discover later in episode 6 ("Loyalty") that he's been researching Inostranka, and by episode 10 ("Everything Will Change"), that's he's a non-human.
Is it possible that Michael knows more about Sean than Sean knows about himself?
So, who is Sean? What is Sean? Is he human? Is he alien? Is he an angel? A hybrid? Is he a sentinel? What do you think?
Stay tuned for more...