Adrian is one of the two Corbo brothers. They are maternal half-brothers, from the same mother but different fathers. Adrian and his older half-brother Jared were raised in the Hull House orphanage, which was actually a facility operated by the Canadian government's secretive agency Department H. There they met Eugene Judd, who was working at the orphanage.
Adrian once had a peculiar flashback to his childhood in Hull House. In the flashback a very young Adrian was holding his teddy bear and calling to Beatrice de la Salle for help. There was a monster with red eyes towering over him. The monster threatened to eat his eyes. Adrian connected this memory with the feeling of being cornered and unable to get away from someone he trusts.
While Adrian was shy, reserved, and bookish, Jared was athletically inclined, aggressive, and arrogant. Both brothers manifested mutant powers after puberty: Adrian gained the ability to transform parts of his body into blades, while Jared manifested a personal force field that could not be deactivated.
According to Jared, the codename "Flex" derives from a childhood nickname for Adrian, used by everyone even before he received his powers. Adrian was the scrawniest kid at the orphanage. One day, during their physical training, Jared decided to tease his brother about it. He asked Adrian to "flex" his muscles and show them off to their class. That night, during dinner, another boy called Adrian "Flex" and the nickname stuck. When the "Frankenstein doctors" of Hull House eventually found out that Adrian's power actually was activated by flexing, they turned the nickname into a codename.
The brothers were recruited into an incarnation of the Canadian superhero team Alpha Flight as Flex and Radius. They assisted Alpha Flight in battling several foes, including the Zodiac, the Brass Bishop, and Department H's own power-mad leader, Jeremy Clarke, who died of radiation poisoning during a Zodiac raid on the Department H headquarters. Their Alpha Flight team fought several members of the original Flight and later teamed up with them to defeat a new Weapon X, created by a rogue Department H scientist. Both groups of Alphans merged into a unified Alpha Flight following this adventure. The Corbo brothers and several other members of the new team were later reassigned to Alpha Flight's trainee team, Beta Flight.
After the events of M-Day, Corbo lost his mutant abilities. His current whereabouts are unknown.
- The identity of the monster in Adrian Corbo's flashback is unclear, though it is implied that the monster was someone who the child trusted. The form of the monster was not humanoid, though it could speak. 
- While Adrian Corbo's monster has very few lines of dialogue, they still form a distinctive pattern: "Help you she can't, young thing! Sure of that I am. Mmmm pretty eyes you have. Eat them I could". This seems to be an inverted syntax, where lines do not follow traditional sentence patterns. 
- The narration of Alpha Flight Vol 2 7 (February, 1998) provides some information on the religious beliefs of Flex. He reportedly believes in heaven. He also believes there are souls inside every living being, souls that call out to each other across the great void of life. 
- The S.H.I.E.L.D. database of mutants known to have lost their mutant abilities during M-Day included Murmur and Radius, but did not include Flex. 
- His astrological symbol is Pisces, so he was born sometime between February 8 and March 20.
- 23 appearance(s) of Adrian Corbo (Earth-616)
- 3 appearance(s) in handbook(s) of Adrian Corbo (Earth-616)
- 28 image(s) of Adrian Corbo (Earth-616)
- 1 quotation(s) by or about Adrian Corbo (Earth-616)