While attending a Legion function with his parents, Garth, along with other heroes, was attacked and apparently killed by the villain known as the Time Trapper. In fact, he was sent to the 30th century. In this era, Garth joined forces with other young heroes on the side of good, collectively known as the Legion of Super-Heroes. Ranzz has also served in the Legion's strike force, the Legionnaires. It is during this period of his career that Garth meets and begins to date Imra Ardeen.
As a result of changes to the time stream resulting from the Crisis on Infinite Earths, Ranzz's parents were now from the planet Colu. His name was changed to just Garth, and now he is the grandson of Vril Dox, the great scientist of the planet Colu and one-time leader of the Controllers. During the Zero Hour crisis, it is revealed that Garth is the host of a living bomb implanted by his grandfather; if the bomb exploded, the entire Solar System would be destroyed. After several adventures involving his fellow Legionnaires and the Teen Titans, the bomb was destroyed and Garth's full potential unleashed.
After Zero Hour, his powers are drastically increased, giving him the ability to manipulate all forms of energy. He becomes overconfident and egotistical, causing tension with his fellow Legionnaires. When the villain Mordru begins to drain the powers of the Legionnaires, Garth is unaffected and absorbs more power from the sun, which he dispels as powerful energy blasts to incapacitate Mordru. When the villain is finally defeated, Garth's powers are restored to their normal level.
The Crisis on Infinite Earths rewrote and drastically altered this aspect of his history. In the Post-Crisis DC Universe, Garth is introduced in a Legion of Super-Heroes comic as the son of a single mother, born with great power which he initially struggles to control. Upon reaching adulthood, he gains complete mastery over his powers and sets out on a quest to learn his origins. Eventually he learns that his father is a being of great power named Zven as part of the Sun-Eater race, and that his conception had been orchestrated by the Time Trapper so that Garth would eventually succeed him as the Time Trapper.
The Time Trapper manipulates events from the shadows to ensure that Garth reaches his full potential, leading the Legion of Super-Heroes and eventually succeeding Trapper as the universe's overseer of time. Garth rebels against his fate, and with the aid of his friend and team leader Rokk Krinn, he manages to defeat the Time Trapper and free himself from his pre-ordained destiny.
During the Infinite Crisis, Superboy-Prime attacks Earth, killing dozens including Legion member Ferro Lad. In response, Garth takes drastic measures to restore both his friend's life and the lost city of Daxam. This draws the immediate ire of the Time Trapper, and the two powerful beings become enemies once more. As the Legion of Three Worlds faces the Time Trapper, Rokk Krinn reveals he has become the new Superboy, which enables Garth to tap into his full potential again and defeat the Time Trapper.
In the "Lightning Saga" storyline, it is revealed that Garth's DNA is a template for the lightning creatures which the Legion encounters. These creatures are attracted to the great amount of energy he gives off, and threaten the galaxy. It is later discovered that the lightning creatures are actually a part of Garth's subconscious mind.
During the events of the "Final Crisis" storyline,Garth aids in the battle against Darkseid and his forces, and is one of he heroes killed when Darkseid detonates the Anti-Life Equation. He does not remain forever in death, however, and is one of the many deceased Legion of Super-Heroes members that are brought back during the "Legion of 3 Worlds" storyline.