Ultraman Jack is the villainous older brother of Father of Ultra, who was envious that his brother was picked over him for the title of the Inter Galactic Defense Force's Top Commander. In retaliation, he started his own "New Inter Galactic Defense Force" and made himself dictator, until he was defeated by his former comrades. He only appeared in the 1979 Tetsuji Kataoka manga Ultra Brothers Story.
Jack was the older brother of Father of Ultra, who was chosen to be the Top Commander of the Inter Galactic Defense Force by Ultraman King. Jealous of his younger sibling's accomplishment, Jack formed the New Inter Galactic Defense Force and declared himself to be Top Commander, though his organization quickly became a dictatorship. The New Inter Galactic Defense Force set out to crush anything Jack considered to be evil, which also consisted of anyone that Jack felt had wronged him. However, his insurrection was eventually crushed and Jack was killed by Ultraseven.