Duke Fleed (デューク・フリード, Dyūku Furīdo) is UFO Robo Grendizer main character. Details about his back-story vary depending not only on the version (manga or anime) but also between the original series.
Duke was the Crown Prince of planet Fleed, a peaceful, idyllic world. His peaceful, comfortable life ended when invading forces of King Vega attacked its planet. Fleed lost the war, the royal family was murdered, and the planet was bombarded with radioactive bombs and turned into a toxic wasteland. Duke managed to seize Grendizer and fled the planet. Grendizer's navigational computer searched a planet with an atmosphere similar to Fleed's, and Grendizer crashed on Earth, near from the Space Science Laboratory. Doctor Umon found Duke, took him in like his son and gave him a new name: Daisuke Umon (宇門大介, Umon Daisuke).
Duke began to work in the ranch his adoptive father owned, under the orders of Danbei Makiba. A while later he had adapted to his life on Earth and his old psychological scars were beginning to knit, when reports of alien saucers scouting Earth started arriving to the Laboratory, and Kouji Kabuto arrived Makiba Ranch...
Duke has several traits on common with the other two male heroes of the Mazinger trilogy, but right like Tetsuya was a different character than Kouji, Duke is his own character. He is older than them; therefore he is more mature and nicer. Duke is very hot-blooded when he is riding his mecha or fighting, but the remainder time he is calm and even quiet… unless something sets him off.