Final answer:
William I is known as William the Conqueror who introduced feudalism in Norman England after originating from Normandy. The Magna Carta and the Domesday Book are key primary sources for understanding this era.
Step-by-step explanation:
The historical figure who is commonly referred to as William I is William the Conqueror, who became the King of England after his victory at the Battle of Hastings in 1066. The Normans originated from the region of Normandy in northern France. In the context of Norman England, the political and social system characterized by a hierarchical structure of land ownership and obligations is known as feudalism.
Primary sources that provide insights into the historical understanding of feudalism in Norman England include legal documents such as the Magna Carta, chronicles written by monks and other contemporaries, and the Domesday Book, which was a record of all the landholdings in England commissioned by William the Conqueror.