William I, Duke of Normandy

William I "Longsword"
Statue of William Longsword, part of the "Six Dukes of Normandy" series in Falaise
Count of Rouen
Reign	927–942
Predecessor	Rollo
Successor	Richard I
Born	c. 893 Bayeux or Rouen
Died	17 December 942 Picquigny on the Somme
Burial	Rouen Cathedral
Spouse	Luitgarde of Vermandois
Issue	Richard I of Normandy
House	House of Normandy
Father	Rollo
Mother	Poppa

William Longsword (French: Guillaume Longue-Épée, Latin: Willermus Longa Spata, Old Norse: Vilhjálmr Langaspjót), (c. 893 – 17 December 942) was the second ruler of Normandy, from 927 until his assassination in 942.

He is sometimes anachronistically dubbed "Duke of Normandy", even though the title duke (dux) did not come into common usage until the 11th century. Longsword was known at the time by the title Count (Latin comes) of Rouen.Flodoard—always detailed about titles—consistently referred to both Rollo and his son William as principes (chieftains) of the Norse.

William Longsword was born "overseas" to the Viking Rollo (while he was still a pagan) and his Christian wife Poppa of Bayeux.Dudo of Saint-Quentin in his panegyric of the Norman dukes describes Poppa as the daughter of a Count Beranger, the dominant prince of that region. In the 11th century Annales Rouennaises (Annals of Rouen), she is called the daughter of Guy, Count of Senlis, otherwise unknown to history. Despite the uncertainty of her parentage she was undoubtedly a member of the Frankish aristocracy. According to the Longsword's planctus, he was baptized a Christian probably at the same time as his father, which Orderic Vitalis stated was in 912, by Franco, Archbishop of Rouen.

Longsword succeeded Rollo (who would continue to live for about another 5 years) in 927 and, early in his reign, faced a rebellion from Normans who felt he had become too Gallicised and too soft. According to Orderic Vitalis, the leader was Riouf of Evreux, who was besieging Longsword in Rouen. Sallying forth, Longsword won a decisive battle, proving his authority to be Duke. At the time of this 933 rebellion Longsword sent his pregnant wife by custom, Sprota, to Fécamp where their son Richard was born.