Eustass Captain Kidd is a prominent figure from the Grand Line, known as the captain of the Kidd Pirates and a leading member of the group of pirates called the worst generation. Hailing from the South Blue, he grew up in a lawless environment where he and his childhood friend, who would become his first mate, ruled over different districts of their home island. His life took a decisive turn when a close friend was killed by a local gang; in response, he united the districts under his rule and set out to sea, forming his own crew and naming his ship in her memory.

Standing over two meters tall with a fiery red, spiked hairstyle and a muscular build, Kidd cuts an imposing figure. After entering the New World, he suffered a major defeat against the Red Hair Pirates, losing his left arm and gaining extensive scars across his torso and face, which he later replaced with a metallic prosthetic created and controlled by his devil fruit powers. His personality is defined by a volatile mix of immense ambition and ruthless aggression. Kidd is notoriously hot-tempered and quick to violence, holding no qualms about harming civilians or any who dare to mock his dream of finding the titular treasure and becoming the next Pirate King. Despite this cruelty, he holds a strong code of loyalty towards his crew, particularly his first mate, and will not tolerate anyone insulting them.

Kidd possesses the power of the Magnet-Magnet Fruit, a Paramecia-type devil fruit that allows him to generate magnetic fields. This ability lets him attract and repel metallic objects, which he can shape into giant limbs for combat or form into complex constructs. He has mastered this power to the point of awakening, which grants him the ability to assign magnetic polarities to other people or objects, forcing them to violently attract or repel each other. His most powerful technique is an electromagnetic cannon that can generate enough force to seriously injure even the most durable of opponents. In addition to his devil fruit, Kidd is a confirmed user of all three types of Haki, including the rare and powerful Conquerors Haki, which signifies his kingly ambitions.

Upon his first appearance on the Sabaody Archipelago, Kidd held the highest bounty among all the supernovas due to his particularly brutal methods. Following the Summit War, he entered the New World, a sea dominated by the Four Emperors. He immediately came into conflict with them, losing his arm to Shanks crew and later being betrayed by an ally and subsequently defeated and imprisoned by Kaido. This chain of events led him to form a reluctant alliance with his rivals, Monkey D. Luffy and Trafalgar Law, to take down the emperors. During the ensuing raid, Kidd played a pivotal role in the victory against one of the emperors, showcasing his full power and awakening. After the battle, his bounty was raised to an impressive sum, placing him on equal footing with his two main rivals as they parted ways to continue their individual journeys toward the ultimate goal.