Ekos was culturally contaminated by the Federation's observer, professor John Gill, in the mid-2260s. Gill abandoned the non-interference policy, and created a Nazi-style world government in which he was the Führer. Melakon became his Deputy Führer, and quickly assumed the worst aspects of the Nazi philosophy, destroying Gill's good intentions and taking real command of the state.
Melakon used the presence of Zeons on Ekos in much the same way as Adolf Hitler used the Jews of Germany and Europe; he made them scapegoats for Ekos' problems and declared them a threat to be eliminated. With the technology elicited from Gill, Melakon rapidly upgraded Ekosian weapons. By 2268 the Final Decision, a genocidal invasion of the planet Zeon, was ready for deployment.
The USS Enterprise, assigned to discover what had happened to Gill, arrived at Ekos just before the launch of the Final Decision. The intervention of Kirk, Spock and McCoy roused the drugged Gill in time to halt the invasion.
Melakon's regime proved to be weaker than the German model; the Nazi government and "Final Decision" was not embraced by all of Ekos. An underground alliance of Zeons and Ekosians had formed, including high-level Nazi party members who wanted no part in the genocide. When Gill ordered a halt in the invasion and declared Melakon a traitor, Melakon shot him with a machine gun for ruining his plans. In return, the Zeon immigrant Isak killed him by shooting him in the stomach with a pistol. (TOS: "Patterns of Force")