Daisuke Umon, alias Duke Fleed, is the crown prince and lone survivor of the annihilated Planet Fleed, destroyed by King Vega’s armies in their quest to seize Vegatron, a radioactive ore. Escaping to Earth aboard the stolen super robot Grendizer—a mechanical incarnation of Fleed’s war deity—he crash-landed near Mount Fuji. Adopted by Professor Umon of the Space Science Laboratory, he concealed his extraterrestrial origins under the guise of a ranch hand at Danbei Makiba’s estate. His true identity remained a closely guarded secret, known only to Professor Umon, Danbei’s children Hikaru and Goro, and Koji Kabuto, ex-pilot of the Mazinger Z. Two years into his life on Earth, Duke’s hidden past erupted when Koji clashed with Vegan forces, compelling him to unleash Grendizer in Earth’s defense. His rivalry with Koji shifted to alliance, bolstered by Hikaru’s unwavering support as a co-pilot. Amid battles against Vegan invaders, Duke encountered Maria Grace Fleed, his long-lost sister, who had survived Fleed’s destruction under the protection of a loyal survivor. Unaware of Duke’s true identity, Maria initially sought vengeance against Grendizer’s pilot until their sibling bond surfaced through shared heirlooms. Reunited, she allied with his cause. Duke’s history intertwined tragically with Princess Rubina, daughter of King Vega and his former betrothed. Learning of Fleed’s restored habitability, Rubina tried to warn Duke but perished in a Vegan ambush, fueling his resolve to dismantle Vega’s tyranny. In the climactic assault, Duke spearheaded Earth’s forces to obliterate Vega’s armada and the tyrant himself. Victorious, he departed with Maria to resurrect their ravaged homeland. Beyond canonical events, crossover media like *Grendizer, Getter Robo G, Great Mazinger: Kessen! Daikaijuu* depict Duke uniting with Great Mazinger and Getter Robo G to thwart the Dragonsaurus, a primordial leviathan endangering Tokyo. These tales, while separate from core continuity, echo his legacy as Earth’s steadfast guardian alongside allies like Koji. Duke’s journey weaves loss, resilience, and allegiance, navigating his dual existence as a refugee prince and Earth’s shield. Bonds with Koji, Hikaru, and Maria chart his evolution from isolated fugitive to collaborative leader, culminating in his return to Fleed—a testament to his unyielding dedication to his people’s rebirth.