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 coallition that halted the "Final Decision" nuclear strike on Zeon, and brought down the Nazi regime. At the introduction, Isak learned that his fiancee Uletta was killed by Nazis. Later, Isak killed Deputy Führer Melakon, shooting him in the belly. (TOS: "Patterns of Force")