Antonio was the right-hand man of Samurai Goroh, but Goroh betrayed and abandoned him into the hands of the Galactic Space Allies. After his release, he became a solo bandit, and now his only purpose in life is to have his revenge on Goroh, ideally in front of millions of fans on the F-ZERO circuit.
Originally Antonio Guster was a longtime friend of Samurai Goroh. After Goroh was dishonorably discharged from the Internova Police Force, he turned to Antonio Guster for information to help with his new bounty hunting career. Antonio quickly took up Goroh on his offer of a new partnership in a career of thievery and bounties. They worked together for three years and their close relationship often got them compared to the Fukikakes, though never to their faces. There was no bounty that these two would turn down, no matter what the creature was.
There partnership reached its end while they were escorting the recently captured evil Lord Kimbo back to their ship on the Takoran Moon. While they were at one of the shanty towns, Samurai Goroh abandoned Antonio and taken Lord Kimbo and cashed in on the bounty. Antonio was captured by the Galactic Space Allies and only escaped with the help of three other prisoners. When he found out what Goroh had done, he swore revenge against his old friend. For that reason he entered the F-Zero races so he could humiliate his old partner in front of millions of F-Zero fans.
In the anime-inspired games F-Zero: GP Legend and Climax, Antonio Guster is the younger brother of Lisa Brilliant. In GP Legend, he tricks Samurai Goroh by poisoning him. Antonio is forced to eventually relent and give Goroh the antidote after losing a race to him.