Aptom is a major character from the Bioboosted Armor Guyver series. He is a "Lost Number", an experimental Zoanoid designed by Cronos' co-founder Dr. Hamilcar Barcas to possess abilities and powers beyond what standard Zoanoids are capable of. Though he worked for Cronos when he first appeared in the series, Aptom was later able to abandon the organisation thanks to Dr. Barcas' extensive over-processing which granted him immunity to the psychic control of the Zoalords. While initially an enemy of the Guyvers, Aptom would join forces with them some time after Cronos' domination of Earth.