Cargo ship crewman Morrie Bench was accidentally knocked overboard by Spider-Man (who was battling Sub-Mariner) during the testing of a powerful new experimental underwater generator, the energies of which combined with gases from undersea volcanoes to trigger a weird mutation in Bench, who began to transform into living water. Physically and emotionally unstable, Bench dubbed himself Hydro-Man and soon attacked Spider-Man, but he evaporated after Spider-Man scattered his liquid form amidst the hot sunshine of the New York rooftops; however, the particles of Bench's body soon reintegrated, and he embarked on a long criminal career.
When Bench and rival criminal Sandman fought over the affections of barfly Sadie Frickett, the two men accidentally merged into a monstrous "mud-thing" that the police were ultimately forced to dehydrate into seemingly inert rubble. Hydro-Man and Sandman eventually managed to separate back into their original forms, but both were humiliated and traumatized by the experience. Sandman was so shaken that he went straight for years (until the Wizard brainwashed him into returning to crime), while Hydro-Man did most of his criminal work in groups from that point on, perhaps seeking safety in numbers.
Both alone and as a member of teams like the Sinister Syndicate, the Frightful Four and the Assembly of Evil, Bench fought a wide array of foes such as Silver Sable, Sandman, the Fantastic Four, Cloak & Dagger, the Avengers, the New Warriors, Thunderstrike, the Thunderbolts, Gambit and Black Panther, but most often clashed with Spider-Man. Hydro-Man was one of many super-criminals employed by corrupt billionaire Justin Hammer for a time, and later served in the Masters of Evil assembled by Hammer's daughter Justine, alias the Crimson Cowl; however, after Justine's arrest and the apparent death of Justin, Hammer Industries phased out its criminal enterprises and Bench, along with fellow employee the Shocker, was laid off. The Shocker and Hydro-Man then teamed up for one last crime, seeking enough money to retire, but Hydro-Man's thirst for revenge against Spider-Man led to their defeat. Trying and failing to go straight, Bench was recruited back into the Wizard's Frightful Four and, more recently, the Sinister Twelve.