Yooden Vranx is the late former President of the Galaxy, the direct predecessor to Zaphod Beeblebrox. Just before his death, Yooden came to see Zaphod and presented his idea to steal the Heart of Gold. Following Yooden's suggestion, Zaphod locked out a section in each of his own brains so that no one could figure out why he ran for the presidency.
Zaphod and Ford Prefect's first encounter with Yooden occurred when they were children on Betelgeuse and Yooden was a ship's captain. Zaphod had bet Ford that he could raid a heavily fortified Arcturan megafreighter and took Ford along for the attempt, using a souped-up trijet scooter. They successfully boarded the ship (captained by Yooden), stormed the bridge with toy pistols, and demanded conkers. Yooden gave them conkers, food, booze, and various other items before teleporting them to the maximum-security wing of the Betelgeuse state prison.
Read more about this topic: Loonquawl