New York native William Baker, often known on the streets as Flint Marko, was a common criminal who spent most of his early life drifting in and out of street gangs and correctional facilities. While on the run from the FBI in Georgia, Baker took a moment to relax on a beach. When the steam system of a nearby nuclear test reactor exploded, it dumped massive doses of radiation on the beach, as well as Baker.

After regaining consciousness, Baker discovered that his body had bonded with the sand around him, and he could form himself into almost anything he desired. With his new found power, Baker called himself Sandman and began a super-powered lifestyle that has brought him head to head with the likes of Spider-Man, the Fantastic Four and the Incredible Hulk.