Henry I, the youngest son of William the Conqueror, ascended to the English throne in 1100. His long reign, which lasted until 1135, was defined by a concerted effort to centralise and strengthen royal government. Known for his administrative reforms, he established a more structured approach to governance, laying the foundations for the development of the Exchequer to manage the crown's finances more effectively.

Throughout his time as monarch, Henry was heavily preoccupied with maintaining control over his ancestral lands in Normandy. This led to persistent conflict, most notably his victory at the Battle of Tinchebray in 1106, which allowed him to secure the duchy and reunite it with the English crown. His foreign policy was largely focused on defending these continental interests against various rivals and securing his borders.

The latter part of his reign was overshadowed by a profound succession crisis. Following the tragic death of his only legitimate son and heir, William Adelin, in the White Ship disaster of 1120, the stability of the future monarchy was thrown into doubt. Henry spent his final years attempting to ensure the succession of his daughter, Matilda, forcing his barons to swear oaths of allegiance to her.

Key aspects of his reign include:

• The consolidation of royal authority and the development of administrative systems.
• The successful acquisition and defence of the Duchy of Normandy.
• The establishment of the Exchequer to oversee royal revenue.
• The struggle to secure the succession for his daughter, Matilda.
• The political instability that followed the loss of his male heir.

Henry I died in 1135, leaving behind a kingdom that had seen significant institutional progress but was ultimately left on the brink of civil war. The failure of the nobility to honour their oaths to Matilda resulted in the period of conflict known as The Anarchy, which began shortly after his death.