Gim was on vacation from the Science Police Academy, hiking on Mars, and was the only one present to witness the crash of a strange glowing meteor. The meteor's radiation altered his genetic structure, giving him the power to grow to a variety of giant sizes at will. Gim's family had a long tradition of police and military service, dating back to a 20th century ancestor who was an Israeli war hero. Gim's parents convinced him that his new poers should not cause him to leave law enforcement, but join the Legion of Super-Heroes instead. Gim said goodbye to the Science Police Academy and to a cadet he'd been dating named Gigi Cusimano. He applied for Legion membership and was accepted, taking the name Colossal Boy.
Colossal Boy served steadily with the Legion, he only lapse being when he was forced to join the Legion of Super Villains when his parents were turned to glass by Tarik the Mute. The Legion eventually investigated the situation and was able to recover and restore Gim's parents.
For several years Colossal Boy had a crush on fellow Legionnaire Shrinking Violet, although the attraction was not reciprocated and he continued to be involved with other women. When a Durlan actress named Yera was convinced to infiltrate the Legion as Violet, she responded to one of Gim's periodic passes and the two were ultimately married. When it was revealed who "Violet" actually was and that Yera had been the dupe of a radical group on the planet Imsk, the marriage was eligible for annulment, but the two chose to make a go of it. The two are happily married, making this the only Legionnaire/non-Legionnaire marriage.
Powers and abilities
Colossal Boy can grow to enormous sizes, and gains super strength the taller that he becomes. At he normal height he has a strength greater than that of a normal human.
Colossal Boy's training with the Science Police gives him a working knowledge of weapons, and a greater knowledge of law enforcement than the other Legionnaires.
- Gim is Jewish. This makes him one of the only Legionnaires whose religion is known.