I can't write anything definitively on this until after 'Lost' is over; I might even have to wait until 'Supernatural' has finished its run as well. But still I wanted to put this out there, submit it foryour approval:
Although he may be stuck in the bodily form of John Locke right now in this final season of 'Lost', the "Man In Black" used to look like the actor Titus Welliver.
Someone else who looked like Welliver was War, one of the Four Horsemen of the Apocalypse, as seen on 'Supernatural'.
Since both beings are of supernatural origin, could it be that there is some sort of connection?
I'm not saying they have to be the same being - their timelines could be overlapping. Then again the Man In Black was stuck on the Island - at least as of 2007. War, AKA Roger, was introduced in 2009. Who knows? Maybe the Man In Black does escape the Island and gets to go home - and resume his career as War. If War had been free to join his fellow Horsemen (Famine, Pestilence, and Death), don't you think the Apocalypse in Earth Prime-Time would have occurred with the new Millennium?
We'll have to wait and view what happens in both shows. At least with 'Lost' we'll have the answers (about the Man In Black at least) after the finale on May 23. 'Supernatural' looks to have a solid run ahead of it still; they can afford to hold off with the answer platter.