From Wikipedia, the free encyclopedia

The title dux et princeps Francorum, or duke and prince of the Franks, was the title adopted by Pepin of Heristal after his epoch-making victory at the Battle of Tertry in 687. Though previously he had been the mayor of the palace of Austrasia (since 680), by defeating a Neustro-Burgundian army at Tertry he extended his authority over the entire Frankish realm, the first mayor ever to do so. In light of this, he adopted the new titular dignity to indicate his supremacy.

The title persisted when his illegitimate son, Charles Martel, used it after conquering the Neustrians at the Battle of Soissons. The title also arose later as equivalent to the title dux Franciae, the title of the rulers of the Île de France, informally Francia. These, the dynasts of Robert the Strong's family, are usually termed "Dukes of France" and their title evolved into the name for the French nation (France) after one of their members, Hugh Capet, ascended the throne.