Castor Gnawbarque III was the CEO of Beavertron Incorporated, a galactic energy corporation. Gnawbarque assumed control of the company after his father, Castor "Bucktooth" Gnawbarque II, died choking on a piece of wet hickory.^[1]

Beavertron planned to build a hydroelectric dam on Tarka's World, but due to Tarkan law, Gnawbarque had to physically possess the deeds to the land in order to begin construction.^[2] Gnawbarque allied himself with Otta Spice, a Tarkan resentful of her people and a one time partner/lover of Rocket Raccoon, to help him acquire the deeds.^[3] Otta convinced Rocket to steal the deed on the pretence of protecting the environment of Tarka's World but she double crossed him and Rocket was sent to a Sekurimax Inc. prison for theft.^[4] After breaking out of prison, Rocket felt compelled to protect the people of Tarka's World and decided to steal the deeds back from Gnawbarque.^[1]

Rocket's prison escape had caused Sekurimax Inc.'s stock prices to drop significantly, allowing Gnawbarque to buy out the company. Sekurimax's CEO Max Sekuri was scheduled to meet with Gnawbarque to complete the sale. With help from the Technet, Rocket disguised himself as Sekuri and infiltrated Gnawbarque's office and managed to get him to open his safe, which contained the deeds. Otta, who was present at the meeting, saw through Rocket's deception and shot him, making him revert to his true form. During the ensuing firefight, Otta accidentally shot a painting on Gnawbarque's wall and Otta knocked him out with her gun when he demanded her to stop shooting. The fight ended when Technet member Gatecrasher punched Otta in the face, knocking her out. Rocket then took the deeds and sent them back to Tarka's World.^[3]

Gnawbarque's subsequent enterprise saw him exploit the headquarters of his own company, Daggett's World. Using a machine called the D-Type Converter that was derived from Galactus' technology, Gnawbarque siphoned life energy off the world's surface under the pretense he was drawing geothermal power. Since the planet started becoming arid and all life on it would ultimately be at risk, the recently-splintered Guardians of the Galaxy were alerted of Gnawbarque's ploy. As part of their plan, the Guardians had Rocket Raccoon dawdle at Gnawbarque's casino to draw his attention. Learning of Rocket's presence, Gnawbarque hired the other half of the Guardians to kill him.^[5] After Hercules sabotaged the D-Type Converter beyond repair, Marvel Boy broke into Gnawbarque's office. He forced into him a pair of Quantum Bands that were tuned to another set worn by Hercules. Once Hercules activated his Quantum Bands, they forced Gnawbarque to switch places with him, leaving the tycoon stranded inside the D-Type Converter seconds before it exploded, killing him.^[6]

Castor Gnawbarque III is amoral and money-driven, to the point he was willing to slowly kill his own planet for profit with the use of the D-Type Converter.^[5] He also seemingly had an unhappy relationship with his late father, who was described as "eager to punish." Before his meeting with Max Sekuri, Gnawbarque stared at a painting of his father and wondered if he would be proud of him.^[1] A paranoid individual, Gnawbarque never left his office at Beavertron HQ, which was located in a tesseract space one micron sideways from reality.^[1]