Isak was a persecuted Zeon male living on Ekos in 2268. Along with his older brother Abrom, he was part of the anti-Nazi resistance.

After meeting Captain Kirk and Spock, Isak introduced the Enterprise officers to the resistance movement, building a coalition that halted the "Final Decision" nuclear strike on Zeon, and brought down the Nazi regime. At the introduction, Isak learned that his fiancée Uletta was killed by Nazis. Later, immediately after Deputy Führer Melakon, killed Führer John Gill (who was his drugged puppet ruler) for exposing his usurpation, Isak shot him dead. (TOS: "Patterns of Force")