Duke Fleed, crown prince of Planet Fleed, saw his world devastated by King Vega's Vegan Empire. His parents perished, and Fleed became a radioactive wasteland. Duke stole the powerful robot Grendizer, meant for Vega, and escaped in a Spazer spacecraft. A Vegatron attack inflicted radiation poisoning during flight. Guided by Grendizer's navigation, he crash-landed near Mount Fuji on Earth. Dr. Genzo Umon rescued Duke, adopting him and giving him the Earth name Daisuke Umon to hide his alien origins. As Daisuke, he worked as a ranch hand for the Makiba family, forming close bonds with Danbei Makiba and his children, Hikaru and Goro. Duke sought a peaceful Earth life, suppressing his traumatic past. Two years later, sightings of Vegan saucers prompted Koji Kabuto, returning in his TFO, to investigate. Duke warned Koji of the Vegan threat, but Koji dismissed him and attempted peaceful contact. When Vegans attacked Koji, Duke revealed his true identity, unearthed Grendizer, and intervened, marking the start of his battle to protect Earth. In civilian life as Daisuke, Duke displayed a calm, reserved, and thoughtful demeanor, contrasting with Koji's impulsiveness. He wore Western-style attire: a brown tasseled vest, yellow shirt, brown pants, and black boots. When piloting Grendizer, he generated a red-and-black armored suit with a knight-like helmet, green visor, and spiked decorations, reflecting Fleedian royal heritage. The suit protected against hazards like lasers and leveraged his Fleedian physiology for enhanced agility and healing. Despite his composure, Duke carried profound guilt over fleeing Fleed and failing to save his family. This trauma drove his determination to prevent Earth suffering a similar fate. Though pacifistic, he fought out of necessity, occasionally exhibiting uncontrolled rage confronting Vegans or recalling his losses. Duke's relationships evolved. He revered Dr. Umon as a father figure and mentor. Hikaru Makiba, discovering his secret, became a trusted confidante and ally, piloting the Marine Spazer despite Duke's initial objections. Koji Kabuto transitioned from rival to close friend and co-pilot, forming a formidable partnership. Duke later encountered Maria Fleed, his younger sister, who initially sought revenge against Grendizer's pilot, believing Duke dead. Matching necklaces confirmed their sibling bond, leading to reconciliation and Maria joining as the Drill Spazer pilot. A pivotal figure was Princess Rubina of Vega, Duke's former fiancée. Their arranged marriage aimed to forge an alliance, but King Vega's betrayal destroyed Fleed. Rubina later located Duke on Earth to warn him of Vegan plots, dying shielding him from an assassin's blast. Her sacrifice intensified Duke's resolve to end the Vegan Empire. In *Grendizer U*, Duke's backstory includes additional complexities. Cassado, a fellow Starker Knight he considered a friend, framed him for his parents' murder. Overwhelmed by rage, Duke inadvertently caused Grendizer to rampage, killing Fleedian civilians and nearly destroying Rubina's ship. Believing he killed her, he fled to Earth with Grendizer, suffering amnesia upon arrival. After Koji and Sayaka Yumi rescued him, his memories gradually returned, deepening his guilt. Koji provided a ring-shaped explosive device as a safeguard should Duke lose control again, symbolizing mutual trust. Duke navigated conflicts with Teronna, his best friend and Rubina's sister, who initially viewed him as an enemy after the rampage, and Naida, a childhood friend sent to assassinate him but who sacrificed herself saving Earth after learning Rubina survived. Duke possessed innate Fleedian abilities: superhuman agility, rapid healing, and the power to summon his pilot suit. He was an expert mecha pilot, adeptly commanding Grendizer and auxiliary vehicles like the Spazer and Dizer trike. His combat style combined tactical precision with overwhelming ferocity, particularly avenging allies or confronting Vegan commanders. The conflict culminated in a final assault against King Vega's forces. Duke, alongside Koji, Hikaru, and Maria, destroyed the Vegan mothership and killed Vega. With the empire defeated, Duke and Maria returned to Fleed to rebuild their home world, bidding farewell to their Earth companions.