One of this ruler's more enduring acts as Prince of Aquitaine was the seizure of Barcelona from the Moors in 801.  As emperor, he was responsible for executing Bernard I, king of Italy, for treason, an act for which he did a 
One of this ruler's more enduring acts as Prince of Aquitaine was the seizure of Barcelona from the Moors in 801.  As emperor, he was responsible for executing Bernard I, king of Italy, for treason, an act for which he did a penance at the request of Pope Paschal I, earning his nickname.  After dealing with three civil wars he died in 840, and the empire founded by his father descended into a civil war between Lothair, Louis the German, and Charles the Bald, this ruler's sons.  FTP, identify this French ruler, son of Charlemagne.
One of this ruler's more enduring acts as Prince of Aquitaine was the seizure of Barcelona from the Moors in 801.  
Louis the {Pious} or Louis I