Dexters meet their much older self, a wizened senior citizen Dexter about the same height as the kid Dexter who is responsible for bringing the world into this new age with his brainpower (and Mandark's brain in a vat who cannot do anything other than complain about his situation). Due to his advanced age, however, Old Man Dexter can't remember anything about how he saved the world, so they travel back in time to find out. In this final time period, which takes place between the first and second time periods, they find a dystopic world where everyone is stupid and fire and technology are forbidden, controlled by overlord Mandark thanks to the Neurotomic Protocore. They meet action hero Dexter, who is tall, muscular and bald, fighting Mandark's evil robots. Action Hero Dexter explains that he and Mandark had been employed as corporate research scientists many years ago, where a jealous Mandark, unable to come up with the ideas Dexter could, stole them and passed them off as his own, using them to rise through the ranks and eventually take over the company in a coup – turning Dexter into the weak, cowardly, cubicle-designing Twelve. Eventually, Mandark got a hold of the Neurotomic Protocore (due to Twelve's mistake in leaving it out in his cubicle) and attempted to harness its power, but set the core's positive flow to negative due to his incompetence with it, twisting his already evil mind. As the Core's now negative energies slowly swept over the world, they gradually numbed the minds of the population and allowed him to take over the world, hoarding all science and knowledge for himself. Dexter, no longer able to stand being enslaved and determined to stop Mandark, spent years digging underground to escape Mandark's tower, growing into his Action Hero persona in the process. By the time he emerged, the world was in its current state. The four Dexters, determined to end Mandark's oppressive rule once and for all, go back to their ruined laboratory and use its resources to build a giant robot to invade his fortress. They manage to fight their way in – though the robot is destroyed in the process – and confront Overlord Mandark, now morbidly obese with brain matter, with his only form of locomotion being carried around his lair by a hook-and-winch. Outnumbered, Mandark evens the playing field by summoning his three selves