Jack and his brother Drake were active members of Stars and Stripes, the citizen’s action portion of Captain America’s Hotline. After Drake became disabled, Jack underwent a physical training regimen, learning several martial arts. When the Serpent Society cheaply bought out the residents of the Sandhaven Acres retirement community after a fraudulent toxic land scare, Jack began investigating. Armed with a “combat boom box” designed by Drake, nineteen year old Jack fashioned a flag-themed costume and intervened when Rock Python and Fer-de-Lance robbed a small bank. Jack, hoping to infiltrate the Society, told King Cobra he wanted to join the group. Cobra, distrusting Jack, sent him to steal from the Reno headquarters of his sometime partner, Mr. Hyde, but also warned Hyde about Jack. Hyde severely beat Flag, who was drenched in Hyde’s chemicals during the fight and developed superhuman strength. Briefly felling Hyde with a desperate blow, Flag contacted Captain America’s hotline and returned to Sandhaven to present Cobra with his stolen loot. Impressed, Cobra tried out Jack in his own King Cobra suit. Captain America soon arrived and Jack allied with him and his protégé, Free Spirit; while the Captain fought Cobra and Mr. Hyde, Jack and Free Spirit defeated the Serpent Society with help from Force Works. Jack followed Captain America and Free Spirit east, aiding them against ULTIMATUM, A.I.M., and Madcap. When Captain America believed himself to be dying, he charged Jack, Spirit, Fabian Stankowicz, and Zach Moonhunter with maintaining the Hotline for him. However, Jack retired his Jack Flag costume after the dissolution of the Hotline.
Recently during the Civil War he donned the costume again to protect civilians from local gangsters and denounced the Registration Act. He was then hunted down by the newly reformed Thunderbolts, a legalized superhero team of former villains. Though fighting valiantly, Jack was paralyzed by Bullseye as he tried to escape through a building and was promptly arrested following the incident. He was thrown into the Negative Zone prison, but during an attack by Blastaar and his minions Jack was rescued by the Guardians of the Galaxy. He underwent surgery to repair his legs, and even though Jack professed to hating everything cosmic he remained with the Guardians as an active member of the group.