Rollo is traditionally credited with founding Normandy after a treaty with the Frankish king in 911.
Rollo was a Viking leader who became the first ruler of Normandy. According to accounts written later, King Charles the Simple granted him territory around the lower Seine in the Treaty of Saint-Clair-sur-Epte, traditionally dated to 911. In return, Rollo accepted baptism and agreed to defend the region against other Viking attacks.
The treaty helped transform a Viking war leader into the founder of a Christian dynasty. The territory granted to Rollo became the foundation of the Duchy of Normandy, whose name derives from the idea of a land of Northmen. His descendants later expanded their influence in northern France and beyond.
The historical Rollo is difficult to reconstruct because the earliest detailed narratives were written generations after his lifetime. Medieval sources also connect him with the Scandinavian figure Hrolf or Gange-Hrólf, but the exact relationship between those traditions remains uncertain. Rollo should not be confused with later Norman rulers such as William the Conqueror.