Short answers, pulled from the story.
Rollo was a Norse war leader who became the first ruler of Normandy, a region in today's northern France, after signing the Treaty of Saint-Clair-sur-Epte with Charles the Simple of West Francia in 911. He is famous as the founder of Normandy and as the great-great-great-grandfather of William the Conqueror, whose Norman Conquest of England in 1066 reshaped medieval Europe.
Rollo's exact origins remain disputed. Dudo of Saint-Quentin identified him as Danish, while the 11th-century monk Goffredo Malaterra and 12th-century historian William of Malmesbury both described him as Norwegian. Icelandic sagas place him from Møre in western Norway. A 2016 attempt to resolve the question through DNA analysis of his descendants' remains failed because the skeletal material did not belong to Rollo's line.
The Treaty of Saint-Clair-sur-Epte was an agreement between Rollo and Charles the Simple, king of West Francia, in 911. Charles granted Rollo lands between the river Epte and the sea; in exchange, Rollo agreed to end his raiding, swear allegiance to Charles, convert to Christianity, and defend the Seine estuary from other Viking raiders.
Rollo earned the nickname "the Walker" because he was so large that no horse could carry him, according to Icelandic sagas that identified him with a figure called Hrólfr the Walker. Snorri Sturluson made this identification in 13th-century texts including the Heimskringla and the Orkneyinga Saga.
Rollo's son William Longsword and grandson Richard the Fearless built Normandy into West Francia's strongest principality. Rollo was the great-great-great-grandfather of William the Conqueror, who led the Norman Conquest of England in 1066. Norman descendants of Rollo's followers also came to rule Sicily and Antioch between the 11th and 13th centuries.
Rollo was formally baptised and took the Christian name Robert, after his godfather Robert I of France. He dedicated portions of his new territory to God, saints, and churches. However, many scholars argue that the conversion was largely formal at first, and that paganism continued to be practiced among his settlers after the official ceremony.