Gyro Zeppeli is a disgraced magistrate and executioner from the Kingdom of Naples (ネアポリス王国 Neaporisu Ōkoku), who participates in the Steel Ball Run to free someone who he believes has been wrongly imprisoned, racing on his horse Valkyrie (ヴァルキリー Varukirī). Gyro is a master of a mystical art called the Rotation (回転 Kaiten), which is channeled through Steel Balls (鉄球 Tekkyū) and is the art of imparting the knowledge of the Golden Rectangle into throwing the Steel Ball, causing the Rotation to be transferred from the ball to the target. It has both healing and offensive properties, as the Zeppeli family has used the Rotation in both their medical practice and in their work as executioners for the church. Gyro later develops a Stand called Scan (スキャン Sukyan) when one of his Steel Balls is imparted with a piece of the Saint's Corpse, the object of desire of Funny Valentine. Scan gives Gyro the ability to look inside people, making his Rotation's attacks even more deadly. With the power of the Super Rotation, accessed by having Valkyrie run at a fast enough speed to make everything incorporate the Golden Rectangle, he develops the Stand Ball Breaker (ボール・ブレイカー Bōru Bureikā), which when a Steel Ball hits its mark the vast energies kept by the Rotation accelerates the life of cells in the target, so much so that the cells die. He is ultimately killed by Funny Valentine.
Gyro's real name is Julius Caesar Zeppeli (ユリウス・カエサル・ツェペリ Yuriusu Kaesaru Tseperi, pronounced in English as Juriasu Shīzā Tseperi (ジュリアス・シーザー・ツェペリ?)), sharing his name with Caesar Zeppeli of Battle Tendency.