Dennis Dunphy was a wrestler who was given super-strenght by the Power Broker. When Captain America fought Superpatriot, another recipient of the Power Broker's superstrenght treatment, he went to investigate the Power Broker's organization and got help from Dennis, who donned a costume inspired on both Daredevil and Wolverine, and named himself Demolition Man, or D-Man for short.
Some time later, when the Commission on Superhero Activities stripped Steve Rogers of his Captain America costume and shield and he became the Captain, D-Man was one of Rogers' allies, alongside Falcon, Nomad and Vagabond. D-Man trained Vagabond in hand-to-hand combat, which Nomad misinterpreted as D-Man hitting on her. When the Captain and his allies faced the Serpent Society, D-Man takes Anaconda down, but Slither attacks him from behind, and while Nomad hesitates from helping D-Man for what happened before, he finally knocks Slither out. After the Captain captures Viper, Cobra finds her and tries to kill her but accidentally frees her due to Nomad's interference, and when Nomad leaves in pursuit of Cobra, Viper pisons D-Man. Diamondback gives D-Man an antidote and tells him to stay there resting. When Battlestar arrives and finds the imprisoned Serpent Society, D-Man mistakenly believes he is freeing them, so they fight, but Battlestar wins and D-Man is imprisoned by the CSA.
Vagabond went with Sidewinder to free D-Man, Diamondback and Nomad, but when D-Man decided that escaping would be wrong, Vagabond staid with him, which caused Nomad to break up with Vagabond. When Rogers turned himself in for his friends' freedom, the CSA freed D-Man as they didn't have use for him.
When the Captain decides to re-assemble the then defunct Avengers, he picks D-Man as his first recruit, who feels honored. Before they can recruit anyone else, Battlestar seeks the Captain's help under his superiors' backs, to free the new Captain America from Flag-Smasher. While Battlestar frees Walker, Flag-Smasher reveals that he needs help to destroy a doomsday weapon created by Red Skull. D-Man crashes a Quinjet against the huge weapon, but seemingly perishes with no body to find.
Some time later, D-Man is found by Falcon and U.S. Agent, who fight some ULTIMATUM agents to retrieve him. Steve is happy to see his friend again, but Dennis is in a sort of catatonic state, never uttering a word. After being attacked and left for dead by his Magus-created doppelganger (from the Infinity War), D-Man stumbled on an underground community of homeless peopleknown as Zerotown and became its protector.