Created by writer Jerry Siegel and artist Jim Mooney, the character first appeared in Action Comics #267 (August 1960).

During the "Five Year Gap" following the Magic Wars, Colossal Boy joins the Science Police as Earth falls under the control of the Dominators and withdraws from the United Planets.

[2] Following Zero Hour: Crisis in Time!, which rebooted the Legion's continuity, Gim Allon is known as Leviathan and originates from a Martian colony.

[4] As Colossal Boy or Leviathan, Gim Allon can increase his size into many times normal height, with strength proportionate in mass.

Gim Allon as Colossal Boy appears as a character summon in Scribblenauts Unmasked: A DC Comics Adventure.