King of England (1100–35). He was the fourth and youngest son of William I. When his brother William II died, Henry seized the treasury at Winchester and was crowned three days later in London, while his elder brother Robert was still on Crusade. Although Robert received the duchy of Normandy in compensation and exacted an annual pension of £2,000 (1101), Henry invaded Normandy in 1106. Robert was defeated at Tinchebrai and imprisoned at Cardiff Castle until his death in 1134. Louis VI of France exploited the situation in Normandy but in two campaigns (1111–13, 1116–20) he failed to take the duchy.

A determined ruler, Henry clashed with Archbishop Anselm over his claim to appoint bishops (lay investiture). He improved royal administration, particularly in the Exchequer, and extended and clarified the judicial systems. His law code, the Leges Henrici Primi, embodied much that had survived from Anglo-Saxon law. Unfortunately the death by drowning (1120) of his only legitimate son William whilst journeying to England from Normandy led to the accession of Henry’s nephew Stephen and a period of anarchy and civil war between Stephen and Henry’s daughter, Matilda.