Lowly TV script writer Stewart Cadwell was visited by the Beyonder not long after the god-like being came to Earth (Secret Wars II #1). Cadwell was awed by the Beyonder and wished he had some of his power, which the Beyonder granted, wishing to learn more about humanity. Transforming into "Thundersword," Cadwell then summoned a winged horse called "Boromir" (named after the character from the Lord of the Rings, just as Valkyrie's own winged horse is named Aragorn) and went on a rampage. He destroyed the places he worked, as well as other cultural institutions he hated, before the X-Men and New Mutants arrived, swiftly followed by Captain America and Iron Man. Thinking that he was the Beyonder himself, the heroes fought and defeated him after a lengthy battle.
Cadwell originally thought he needed a lightning-shaped trophy (which was in his office when he met the Beyonder) to turn into Thundersword. However, when he was in prison (Iron Man #197), he realized that since he had originally conceived his Thundersword powers out of his own imagination, he could perhaps re-imagine his powers in such a way that he no longer needed his award to transform. It worked. He turned into Thundersword and broke out. He fought Iron Man (Rhodey Rhodes) and quickly defeated him. Then he went off to wreak more destruction upon Hollywood.
Rhodes thought he was vastly out-powered and asked Tony Stark's advice. Tony was originally going to fight alongside him by wearing a second suit of Iron Man armor, but they eventually decided to use a second strategy.
Rhodey caught up with him just as Thunderstrike was about to destroy a civilian jetliner. He got Thunderstrike to follow him, then flew to a nuclear power plant where he powered up his armor far beyond its normal capacity. He punched Thundersword so hard that he flew into the sea. However, when Iron Man went to investigate there was no sign of Cadwell. Thundersword has not been seen since.
Powers and Abilities
Thundersword possessed superhuman strength and durability. He was able to shrug off bullets.
Thundersword possessed a lightning fashioned sword that had the ability to cut and slice through metal as well as fire bolts of electricity. It was able to easily destroy concrete walls, cars, and buildings. The sword was powerful enough to incapacitate Iron Man with one blow. He could use it to deflect or absorb Iron Man's repulsor blasts with ease.
His powers, given to him by the Beyonder, were based on his own conceptualization of what a hero should be like. At one point he changed those powers to be more advantageous. Theoretically, he might be able to reconceptualize his powers any way he wants.
He has a flying horse that can seemingly appear out of nowhere.