Because he conquered England.
William (1027-1087 AD) was King of Normandy and conquered England in 1066, becoming known as William the Conqueror (William I of England).
William of Normandy, later known as William the Conqueror--
William I also known as William the Conqueror, William of Normandy, and William the Bastard.
There were two Dukes of Normandy named William: William I Longsword was the 2nd Duke of Normandy. William II the Conqueror was the 7th Duke of Normandy (also known as King William I).
William, Duke of Normandy, who become known as William the Conquerer after he became King of England.
He was known as WIlliam of Normandy, William the Bastard, or William the Conqueror.
Anglo-Saxon England was conquered by William, Duke of Normandy, also known as William the Conqueror.
Normandy
William of Normandy became William the Conqueror.
She was the Great Aunt of William the Conqueror-Duke of Normandy.
William, Duke of Normandy, beat King Harold and his Anglo-Saxon army at Senlac Hill near Hastings in October 1066. He was then known as William 1 and William the Conqueror.
No, he was the Duke of Normandy.