Bubo (died 734), also spelled Bobbo, Poppo or Popo, was the pagan duke (dux) of the Frisians in the early eighth century. He is the first ruler whose name is known after Radbod (died 719). He did not recognise Frankish supremacy, and his territory probably only encompassed the north of Radbod's Frisia. He was defeated in a short war by the forces of Charles Martel, the duke of the Franks, in the Battle of the Boorne. The Frankish chroniclers, such as the Continuations of Fredegar, Vita Willibroridi of Alcuin and the Annales Mettenses priores, depict Bubo as a rebel and the Frankish invasion as a just war.