Dying and living again
Prior to being born as Thom Kallor, Star Boy's soul lived at least two lives on Earth in the 19th and 20th centuries - as the hero Scalphunter in the Old West of the United States of America; then in Opal City as the corrupt policeman Matt O'Dare, a member of a whole family of policemen and belated ally of Jack Knight, one of many heroes to take the name "Starman."
Born again on Xanthu in the late 30th century, Thom Kallor would grow to become one of Xanthu's heroes, the Amazers, with the power to increase the weight of objects and to fly, and when first seen, was in competition to become Xanthu's Planetary Champion for a year. Reaching the final three against Atmos and Kid Quantum (James Cullen), his chances were improved by Kid Quantum's abrupt withdrawal from the competition when he was drafted into the newly-formed Legion. It is not known if he succeeded, but the fact that he was the one tapped as Kid Quantum's replacement after his death would seem to make that unlikely.
Following the Amazers' successful rout of an invading group of Algamenon raiders, he was summoned to replace KQ as the Xanthian draftee on the Legion. Seeing this as an opportunity to face the "hard challenges", he faced hostility from his teammates, who thought that he was glory-seeking. Jazmin Cullen, her brother's replacement as Kid Quantum, was especially hostile to all things Legion-related after James' death, and arranged for "something to remember the Amazers by" - his least favourite music, "Durlan space-shanties", locked on his ship's entertainment system. At full volume.
Three days later, he diverted to Rimbor in a desperate attempt to fix it. After being rooked for most of his savings when the mechanics found other things to "fix", he was knocked for a loop by a group of criminals escaping from Winath after an attempt to kidnap their presidents had been foiled by a pre-Legion Spark. Unable to regain control of the "repaired" ship, he managed to foil their escape by slowing them with a "mass-blast". However, with his ship's power failing, he drifted into an asteroid belt which was being mined, and his ship was destroyed. He was retrieved, barely alive, by the miners, and woke up in neck-to-toe plaster and bandages in their infirmary. After he objected to the miners' shooting of a space whale, they arranged for him to have some of its' blubber mixed in with his food, unbeknownst to him. As a result, he began to heal rapidly, with only his wrists and hands remaining in plaster by the time the miners reached port on Earth.
He arrived at the same time as Gates, a reluctant draftee who had "escaped" from Leviathan during an earlier attempt to draft him; sparking a fight between Cosmic Boy and Leviathan over the former picking a "bed patient and a revolutionary because the President said to" over "good, solid candidates". Afterward, Thom wryly noticed to the team's new intern, Chuck Taine, that "more than just the building" needed fixing.
In his first training session, he knocked Chameleon through the floor of the Legion HQ gymnasium. Leviathan's subsequent annoyance at further damage to their already badly-damaged headquarters led to his first destructive manifestation of space whale-derived power, when he accidentally blasted Cham with electric vision and was unable to stop. He was stopped and saved from a pounding from Gim by Gates, who teleported him into the gym's swimming pool.
Powers and abilities
Currently, the power to control gravity. He can make increase or decrease the pull of gravity on objects, making them rise or fall; he can also compress objects into super-dense materials and use his abilities to fly. This was the result of him practising his powers; originally he was just able to increase the mass and density of objects and make the heavier and harder to move.
Formerly, he also had super-strength, enhanced durability, super speed, electric vision and possibly heightened senses and reflexes.
In at least one version of his future, Star Boy would indeed fulfil the Shade's prediction, time-travelling to the 21st Century to become Starman under the name "Danny Blaine," using a slight variation on the Kingdom Come Starman's costume.
On the second-last day of his life, this Starman would use a Time Bubble to go to 1951, retrieving Jack Knight from a time-travel adventure of his own and returning him to his own time. After briefly reminiscing with Jack on his meeting with him while a teenager in the late 30th Century, saying how he felt he had lived two whole lives, and raising the prospect that he may have been from "a future" rather than "the future," the elderly, scarred Thom/Danny returned to his then-home time to face his fate.
He would never discover that he was the reincarnated Matt O'Dare.