The origin story for Iron Man in a nutshell (from what I remember, not checking Wikipedia for this):
Tony Stark is an arms/technology manufacturer. He gets captured by enemy forces while traveling abroad and he suffers a chest injury that leaves shrapnel close to his heart. He and another scientist construct the Iron Man suit to keep him alive, and he turns it into a weapon and escapes.
Back home he continues running his company while constantly building new and improved Iron Man suits (which is why the suit's design is constantly changing) and turning Iron Man into his company's spokesperson (and a superhero, obviously). Nobody knows that it's actually Stark inside the suit, everyone thinks it's one of Stark's bodyguards.
Later on, they gave him an alcohol problem and he lost his company and his best friend/bodyguard took over the suit for a while. He was also paralyzed for a while after being shot by a crazy ex and the only way he could walk was with the Iron Man suit. Dunno what else they've done with his character lately.