Haven't I seen the main guy before?
Yes! That's Norman Reedus, who you probably recognize from The Walking Dead. Here, the actor plays Sam Bridges, "a man who delivers" tasked with carrying stranded remnants of the future in order to "reunite the shattered world one step at a time." He's a delivery man who retains unknowns called DOOMs and has a phobia of being touched, and is said to be a unique outlier when it comes to "timefall" and how others are aware of its existence.
Some theories classify Sam as a teleporter who can shift back and forth between the purgatory world and what he calls home while others label him as a "Returner," someone who can survive "annihilations" and the process in which a subatomic particle collides with its own antiparticle to produce more particles. There's still a million questions as to why he's carrying living, breathing humans across post-societal environments, or the fact he may be a prisoner of a pre-existing life and set of responsibilities, and we probably won't get answers for them until release. Kojima is determined to make Sam Bridges feel like a real person rather than a lifeless avatar, and as he noted at the Tribeca talk, he's doing whatever he can to "put every aspect" of Reedus in there.
"You will see Norman as Sam in the game and you'll see his acting, and you'll enjoy that," said Kojima. "You have to become Norman when you play. And Norman says a lot of things that you'll probably feel, playing as Norman. So he's Norman and Sam at the same time."