Stewart Cadwall was a Hollywood screenwriter whose career was not going well. While he was arguing with his agent, he inadvertently attracted the attention of the omnipotent alien the Beyonder, who had travelled to Earth to study humanity. Cadwall was impressed by the Beyonder's powers, so the Beyonder imbued him with powers of his own. A lightning-shaped award Cadwall was clutching was transformed into a sword, and Cadwall imagined a more powerful, armored form for himself, along with a winged horse to ride, and called himself Thundersword.
Thundersword left a path of destruction in his wake, attacking a television studio and fast food outlets. He was soon opposed by members of the X-Men, New Mutants, Dazzler, and the Avengers Captain America and the then Iron Man. Captain America disarmed Thundersword, turning him back into his physically unimpressive normal form. Cadwall was taken into police custody.
However, Cadwall soon realized his power was not dependent on his sword, and transformed into Thundersword, breaking out of jail. Iron Man fought him again, unsuccessfully, until thanks to a power boost from an electrical generator, he was able to send him into the Pacific, defeating him. Cadwall's current whereabouts are unknown.