William I, also known as William Longsword, was the Duke of Normandy from 927 until his assassination. His leadership was instrumental in consolidating power in Normandy, transforming it into a prominent political entity. Throughout his reign, William navigated complex relationships with both the Frankish kings and local nobility, often through a combination of military prowess and strategic marriages. The period leading up to his assassination was marked by growing tensions among rival factions within the region, many of whom sought to increase their own influence at the expense of the Duke's authority.

On December 17, 942, William was killed in a violent betrayal. It is widely believed that he was ambushed during a meeting with a group of nobles who initially appeared to support him but had ulterior motives. The specifics of the assassination are not thoroughly documented, but reports indicate that it was a coordinated effort by his enemies, accentuating the volatile political climate of the time. Following his death, Normandy experienced a power vacuum that led to further conflicts among those vying for control, ultimately shaping the future of the duchy.

William's assassination had implications far beyond his immediate circle, affecting the balance of power in Normandy and its interactions with the Kingdom of France. His son, Richard I, ascended to the duchy shortly after, but his rule faced ongoing challenges amid the power struggles that erupted among the Normandy nobility, as well as with the Capetian kings of France. The event marks a vital chapter in the history of Normandy, illustrating the fragile nature of power and influence during the medieval period.