Rollo (died 933), also known with his epithet, Rollo "the Walker", was a Viking who, as Count of Rouen, became the first ruler of Normandy, a region in today's northern France. He emerged as a leading warrior figure among the Norsemen who had secured a permanent foothold on Frankish soil in the valley of the lower Seine after the Siege of Chartres in 911. Charles the Simple, king of West Francia, in what is called the Treaty of Saint-Clair-sur-Epte, granted Rollo lands between the river Epte and the sea in exchange for Rollo agreeing to end his brigandage, swearing allegiance to him, religious conversion and a pledge to defend the Seine's estuary from other Viking raiders.

Rollo's life has been depicted in Dudo of St. Quentin's account. He has been analyzed by European scholars such as W. Vogel, Alexander Bugge, and Henri Prentout, who have debated if Dudo's account can be taken as historically accurate. Rollo's origin and life is heavily debated among different scholars and there is not a clear account of what truthfully happened.

The name Rollo is first recorded in a charter written in 918 as the leader of a group of Viking settlers, and he reigned over the region of Normandy until at least 928. He was succeeded by his son William Longsword in the Duchy of Normandy that he had founded. The offspring of Rollo and his followers, through their intermingling with the indigenous Frankish and Gallo-Roman population of the lands they settled, became known as the "Normans". After the Norman conquest of England and their conquest of southern Italy and Sicily over the following two centuries, their descendants came to rule England, much of Ireland, Sicily and Antioch from the 11th to 13th centuries, leaving behind an enduring legacy in the histories of Europe and the Near East.