Isaac

A wide, blackened scar slashes down across his right eye from the brow, marking the face of this towering figure, who also carries a cleft chin and a faint brown beard behind a pair of glasses. His backswept hair blends blue and brown shades, with one loose blue strand falling along the left side. Under black gloves he hides mechanical hands, and his outfit layers a white lab coat over a green collared shirt, orange tie, and a high tipped coat lined inside with brown fur. His battle gear is a powered exoskeleton of blue and gold plating that gives off a yellow glow, with wired shoulder plates, gauntlets, and knee guards. In his youth his hair was entirely blue, his chin clean, and the facial scar still unpainted.

Grim and consumed by spite, Isaac built his life around striking back at the World Government, which he blames for seizing his home to mine Dyna Stones and for the death of his and Jeanne's mother. That loathing widened to include pirates, whom he rates as no better than the authorities he hates. His thirst for payback eroded his conscience until he was prepared to throw away the islanders, and even exploit his own sister, to achieve it. Jeanne remembers a gentler man who once cherished the island and its people. As both a scientist and a senior officer he is exceptionally sharp, weaving intricate schemes and wielding advanced machinery. When Luffy calls him a coward for sealing himself in armor and abandoning Jeanne, the words land, and his beaten state slowly revives the kinder person he had buried.

Born to the ruler of what was then called Jewel Island, Isaac watched his mother die in a Dyna Stone blast during a pirate raid roughly twelve years earlier, an event that left the scar on his face. He departed to enlist with the Marines, climbed the ranks, and learned how corrupt they were and how they had engineered that very attack. Returning as prison warden, tasked officially with excavating the island's Dyna Stones, he spent a decade quietly assembling revenge. He raised two extra prisons to mass-produce robots, lured the Germa 66 and pirates into his scheme, and spread rumors of buried treasure, all to set off a war and ultimately crash the floating Sky Prison and its Dyna Stones into Mary Geoise.

During the events of World Seeker, Isaac welcomes the captured Luffy before their first clash, overpowering him with Seastone-tipped hands. He duels Zoro to harvest combat data, then turns one of his inventions on Jeanne, converting her into a robot. The plot peaks aboard the Sky Prison, where Luffy shatters his armor in battle. Hearing how deeply Jeanne values the island over vengeance, Isaac softens, hurls Luffy clear, fits his armor onto his sister to launch her to safety, and rides the prison down as it detonates so no one can claim the stones. Revolutionary Army agents, acting on Sabo's word, pull him from the sea, and Jeanne later finds him alive at their mother's grave.