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Official Site: Marvel Entertainment

Jack Flag (Jack Harrison) is a fictional character in the Marvel Comics universe. He first appeared in Captain America (1st series) #434 (December 1994), and was created by Mark Gruenwald and Dave Hoover.

Jack and his brother, Drake, were members of Captain America's computer hotline network and they created a citizen's patrol group in their hometown, Sandhaven, Arizona. Drake was attacked by a couple of criminals and the attack left him unable to use his legs. After the attack, Jack and Drake discovered that the Serpent Society had infiltrated their hometown and they had attempted to contact the local authorities, but the Serpent Society had paid them all off. Jack was unhappy with this information so he began training in the martial arts and weight lifting so that he could fight the Serpent Society himself. He took on a disguise that he thought would make Captain America proud and began to fight crime as Jack Flag.

During a bank robbery, Jack intervened and stopped Rock Python and Fer-de-Lance (both of whom were members of the Serpent Society). Shortly after this, Jack attempted to infiltrate the Society, but King Cobra did not fully trust Flag. King Cobra sent him to rob a painting from Mr. Hyde, who severely beat Jack. While fighting, Flag was drenched in Hyde's chemicals and developed superhuman physical prowess. After receiving his new powers, Flag easily defeated Mr. Hyde and retrieved the painting that he was supposed to steal for the Serpent Society. Before returning the painting to the King Cobra, Flag contacted Captain America's hotline and informed them that the Serpent Society was in Sandhaven. Impressed that he was able to defeat Mr. Hyde, Cobra tried out Jack as a new King Cobra. While Flag was undercover with the Serpent Society, Captain America, and his protégé, Free Spirit, showed up to aid Jack and defeat the Society. Jack followed Captain America and Free Spirit east, aiding them against ULTIMATUM, AIM, and Madcap. When Captain America believed he was dying, he charged Jack, Free Spirit, Fabian Stankowicz and Zach Moonhunter with maintaining his hotline.

Jack Flag helps a girl escape a group of gangbangers and is targeted by the new Thunderbolts for violating the Superhuman Registration Act. He is able to subdue almost all of the Thunderbolts team, but is then stabbed in the spine by Bullseye while escaping, puncturing his cauda equina and apparently leaving him paralyzed, with Bullseye stating that Flag would "Never walk again". He is then taken into custody, where he is severely beaten by an enraged Swordsman.

Jack Flag has not been a contender in any CBUB matches.