William Baker became a crook in his youth but didn't want his mother to know about it, so went by the alias Flint Marko while doing jobs. One day on the run from his latest heist, he briefly stopped at an empty beach to hide. Unfortunately, the beach was empty because the military was testing a nuclear bomb there. Caught in the explosion, Baker had his body molecules bound with the sand around him, turning him into a literal sandman. Since then, the grainy villain clashed with Spider-Man many times, though, in more recent years, he's gotten away from the supervillain gig, and taken on more heroic stances.