Thunderbunny, alias Robert (Bobby) Caswell, is an American action-hero based in Boston, Massachusetts. Bobby transformed into Thunderbunny, a humanoid rabbit with super-powers, by clapping his hands together and picturing Thunderbunny. To transform back, Bobby must create a clear mental picture of himself, but because this is very difficult to do, Bobby is reluctant to use the power. Thunderbunny could fly, was invulnerable, and had super-strength. [“The Sound of Thunder,” Charlton Bullseye v2 #6]
Bobby Caswell was a normal high school student and fan of comic-books who lived with his uncle (a comic-book artist) and aunt. In the summer of 1980, Bobby was staying at his Uncle Al's rented cabin near Rutland, Vermont, when he witnessed something fall from the sky by Bald Mountain. Bicycling out after it, he discovered a crashed extraterrestrial spacecraft, which he entered and activated a communication device. His mind was filled with images of an alien world and a humanoid dog named Dr. Bar-Ko, director of the Energy Institute, who explained that his world was dying and no one was able to stop it. Instead, they sent the energy force of their superhero to benefit another world within a power box. All Bobby had to do to become Thunderbunny was concentrate on him when clapping his hands. After first becoming Thunderbunny, he stopped a robbery in Rutland and was at first thrilled to be an action-hero, until he realized that he was a humanoid bunny and found it difficult to transform back into himself. Finally, he managed to transform back into Bobby with great difficulty.
He apparently did not become Thunderbunny again until December, 1981, when he saved the life of a construction worker in Boston. In his most famous adventure, Thunderbunny encountered Golden Lad, a teenage mystery-man from the 1940s who was the same age as he was when he disappeared in 1946. After Golden Lad was shot by a criminal's laser cannon, he immediately aged to his true age and lost his powers. Thunderbunny saved his life just in time and learned from the now-elderly Golden Lad that others like him had been kept in suspended animation since the 1940s by the Keeper. A few weeks later, Thunderbunny battled the Cosmic Adaptoid Mechanism (CAM), invented by Prof. Peter Pini of the Massachusetts Institute of Technology (MIT).
In an untold tale, Thunderbunny teamed up with Captain Atom to stop an extraterrestrial invasion of Boston.
Thunderbunny “died” under unknown circumstances during the Crisis on Infinite Earths in July, 1985, during a mission to save the Controllers from agents of the Anti-Monitor. Bobby Caswell survived and was again an ordinary young man after being an action-hero for five years.
In December, 1985, energies that were the essence of Thunderbunny were restored unknowingly to Bobby Caswell by Stardust II, a Spanish action-hero and member of the Paragons who gained his own powers by temporarily housing Thunderbunny's energies released during his death, thanks to Stardust the Super-Wizard. As of this writing, Caswell still does not know that the power to transform into Thunderbunny has been restored to him.