Gim Allon was born the only son to Wynn and Marte Allon of Earth. He was raised in a patriotic and Jewish family. As a young man, Gim enrolled in the Science Police Training Academy to become a member of the Science Police. While on vacation on Mars with fellow cadet and childhood friend Gigi Cusimano, a strange meteor crashed into the soil near him. The meteor's radiation altered his body's RNA, giving him the power to grow to giant sizes at will. For a short time he used this power to aid him as a Science Police cadet, nearly apprehending the villain who would go on to be the second Starfinger, but his parents encouraged him to pursue justice in other avenues. He joined the Legion of Super-Heroes as an early recruit, alongside fellow applicant Chameleon Boy, whom Gim gave his codename as the other boy reminded him of a chameleon that Gim had as a boy for a pet. The pair were sworn in together and Gim took the name Colossal Boy, Cham and Gim remained good friends throughout their careers and Gim also later became close friends with fellow Earthling, Sun Boy.
Colossal Boy was created by Jerry Siegel and Jim Mooney.
Original Continuity: New Earth
Gim's tenure with the Legion was one of the most unbroken of any Legionnaires. At one point, his mother was turned to glass and Gim was blackmailed into flubbing a mission, which earned him additional training in the Legion Academy for a time until his mother was saved. Marte, Gim's mother, was eventually elected President of Earth and during her tenure she was notorious for supporting the Legion and allowing the United Planets to assist them where they could. Gim had a crush on fellow member Shrinking Violet that was not reciprocated, then one day the two began to find a new-found connection and enjoyed a romance. Caught in a whirlwind relationship and delighted to have Vi finally reciprocate, the two Legionnaires soon eloped and were married.
Outside of fearing his mother's wraith for not having a traditional marriage, Gim was the happiest he could recall. Shortly thereafter though, it was revealed that Shrinking Violet had actually been replaced by a Durlan actress named Yera. Yera had been hired to infiltrate the Legion and it was she, not Shrinking Violet, who had fallen in love with Colossal Boy. Despite the deception, Yera had been duped into the infiltration and Gim quickly accepted the fact that it was Yera he had come to love so quickly, not Shrinking Violet. She offered Gim divorce, but he refused.
Gim Allon's origin during the new, rebooted universe was similar to before with one exception: he was now a denizen of Mars. He was still raised by Jewish parents and was childhood friends with Gigi. She was still present when he received his powers, this time from a meteor that crashed on Mars while Gim and Gigi were in pursuit of a criminal. Becoming a full fledged officer of the Science Police on Mars, Gim was actually reluctant unlike his previous counterpart to get pulled from S.P. duty to become Mars' official draftee into the new Legion of Super-Heroes as Leviathan. Due to his Science Police training, he was named Legion leader on his first day over founder Cosmic Boy. A "yes man," Gim didn't argue even when he could sense the disdain the founding Legionnaires had for him.
On his first mission as both Legionnaire and leader, fellow draftee Kid Quantum was killed by the villain Tangleweb. This caused Gim to resign as both leader and Legionnaire in shame, though Cosmic Boy insisted he stay on the Legion, as well as hold a grudge against Tangleweb. He eventually apprehended the villain and served as Legion deputy leader for the team's first year. He had a crush on teammate Kinetix, much to the dismay of Shrinking Violet who in this reality had an unrequited crush on Gim. He was hard on fellow Legionnaire Star Boy, likely because he was Xanthu's replacement for the deceased Kid Quantum who died on Gim's watch. During a battle with Dr. Regulus early in the Legion's second year, Leviathan uprooted a dangerous gas main and blasted it point blank at the villain to stop him. The ensuing radiation poisoning killed the villain, but Gim as well. He died telling Shrinking Violet that dying in the line of duty had always been his heart's desire. He was buried on Mars at a traditional Jewish service.
In this reality, Gim Allon was from Earth but has different ancestry. He was born to a race of giants and had a genetic mutation which allowed him to shrink to a 6' height. This ability allowed Gim to interact with the average height Earthlings, whom he fell in love with, and where he learned of and eventually joined the Legionnaire movement. Gim took the codename Micro Lad due to his shrinking ability, though most Legionnaires called him Colossal Boy due to the fact it seemed to them that growing to his 'normal height' was actually the super power. Sometimes considered to be a little on the dim side, Colossal Boy was still a great friend and regarded highly by many Legionnaires.
He even allowed the Legion to stay at his giant-sized house for a time. He was romantically interested in Atom Girl, aka Shrinking Violet. His fondness for calling the Legionnaires "little people" was a cause of turmoil for his friendship with the size-conscious girl.
Retroboot: New Earth
A close analogue to the pre-boot Legion of Super-Heroes was restored to continuity following Infinite Crisis. All events of Gim Allon's life are the same as before the "Five Years Later" storyline. Gim has remained one of the Legion's longest serving members and is still married to Yera, now going by the codename Chameleon Girl and heroing herself. He was one of the few Legionnaires left on Earth during Earth Man's takeover due to his Earthling heritage and was instrumental in defeating Earth Man and saving Superman. Due to Earth Man's imprisoning of best friend Sun Boy and attacking his wife, Gim had reservations about Earth Man joining the Legion but eventually warmed up to him.
Major Story Arcs
Original Continuity: New Earth
Five Years Later
Gim's tenure with the Legion continued until the team was disbanded years later after Magic Wars. Afterwards, Gim rejoined the Science Police and would eventually be promoted to Chief. He stayed with the Science Police even after the Legion reformed, though assisted them when needed.
Powers and Abilities
Gim Allon has the ability to enlarge his body proportionately, effectively growing to sizes from his normal height to heights of ten or twenty five feet, for example. The precise limitations on this power have not been established, nor the exact extent to which his strength increases with size, an apparent side effect of the growth. When Gim loses consciousness, he is returned to his normal size. In the threeboot continuity, Gim was actually from a race of giants and his ability was that he could shrink to a 6' height rather than the other way around. Gim's baseline height was never stated, but he could now only size-shift between these two dimensions instead of having an untold upper limit.
As a Legionnaire, Gim has completed personal combat training and wears the Legion flight ring to fly. The ring also serves as a communication and projection tool. With his additional combat training from his studies with the Science Police, he is one of the most skilled hand-to-hand combatants in the LSH and familiar with law protocol.
Five Years Later / Batch SW6
Shortly thereafter, duplicates of the Legionnaires from their early days surfaced as part of a Dominator experiment, including one of Colossal Boy. This young hero and his team went on to become the Legionnaires of New Earth, with the younger Gim taking the codename Leviathan. Leviathan had a crush on Gossamer instead of Shrinking Violet this time. When Legionnaires past and present confronted Glorith and Mordru to save Cosmic Boy, Gim and the younger Leviathan responded to the call. During this encounter, Leviathan was aged to dust by Glorith. As a result of Leviathan's death, the elder Gim Allon faded from existence, confirming a timeline link between the Legionnaires and the adult Legion.
Justice League Unlimited
Gim appeared as Colossal Boy and as a Legionnaire in the Justice League Unlimited episode "Far From Home." He had no speaking lines and was one of many Legionnaires possessed by the Emerald Eye.
Superman & the Legion of Super-Heroes
In the Legion cartoon, he was a supporting character and often appeared in the background or with few speaking roles. He made sizable contributions to missions in the first season episodes "Lightning Storm" and "Chain of Command" where he was voiced by James Arnold Taylor. During the second season he had no speaking roles and often served under Cosmic Boy. He was one of the Legionnaires who chased Timber Wolf in the episode "Cry Wolf" and was the first to be digitized by Brainiac in "Dark Victory." He was later restored and continued to serve with the Legion.