count of Flanders (988–1035) who greatly expanded the Flemish dominions. He fought successfully both against the Capetian king of France, Robert II, and the Holy Roman emperor Henry II. Henry found himself obliged to grant to Baldwin IV in fief Valenciennes, the burgraveship of Ghent, the land of Waes, and Zeeland. The count of Flanders thus became a feudatory of the empire as well as of the French crown. The French fiefs are known in Flemish history as Crown Flanders (Kroon-Vlaanderen), the German fiefs as Imperial Flanders (Rijks-Vlaanderen). Baldwin's son—afterward Baldwin V—rebelled in 1028 against his father at the instigation of his wife, Adela, daughter of Robert II of France; two years later peace was sworn at Oudenaarde, and the old count continued to reign until his death.

king of Jerusalem (1174–85), called the “leper king” for the disease that afflicted him for most of his short life. His reign saw the growth of factionalism among the Latin nobility that weakened the kingdom during the years when its greatest adversary, the Muslim leader Saladin, extended his influence from Egypt to Syria.

Educated by William, archdeacon of Tyre, Baldwin was crowned four days after his father died. Too young at age 13 to rule the kingdom, he was assisted by his kinsman Raymond III, count of Tripoli, who acted as his regent until 1176. Baldwin's health steadily deteriorated, requiring periodic appointment of other regents and contributing to power struggles among the nobility.

In November 1177 Saladin marched from Egypt to attack Ascalon, and Baldwin rushed to the aid of the city. Trapped within its fortifications, he broke out and defeated Saladin near Mont Gisard. A two-year truce was arranged in 1180, but, soon after it expired, Saladin captured Aleppo (June 1183), thus completing the encirclement of Jerusalem.

In an attempt to keep the succession to the throne in his family, the childless Baldwin crowned his nephew King Baldwin V in November 1183, naming Raymond of Tripoli and Jocelin III of Courtenay the boy's guardians.