Baldwin IV (French: Baudouin; 1161–1185), called the Leper, was King of Jerusalem from 1174 until his death. He was admired by his contemporaries and later historians for his willpower and dedication to the Latin kingdom in the face of debilitating leprosy, which eventually left him blind and unable to use either his hands or his feet. Choosing competent advisers, Baldwin ruled a thriving realm and succeeded in protecting it from the ambitions of Egyptian ruler Saladin.

Baldwin developed the first symptoms of his leprosy as a child, but was only diagnosed after his accession on the death of his father, King Amalric. Thereafter his hands and face became increasingly disfigured. Count Raymond III of Tripoli ruled the kingdom in Baldwin's name until the king reached the age of majority in 1176. As soon as he assumed government, Baldwin planned an invasion of Egypt, which fell through due to his vassals' uncooperativeness. Saladin in turn attacked Baldwin's kingdom in 1177, but the king and the nobleman Raynald of Châtillon repelled him at Montgisard, earning Baldwin fame. The young king mastered horse riding despite gradually losing sensation in his extremities and was able to fight in battles until his last years.

Leprosy precluded Baldwin from marrying. He hoped to abdicate when his sister, Sibylla, married William of Montferrat in 1176, but William died the next year. In 1180, in order to forestall a coup by Count Raymond III of Tripoli and Prince Bohemond III of Antioch, Baldwin had Sibylla marry Guy of Lusignan. Guy was opposed by a large fraction of the nobility, and soon permanently impaired his relationship with Baldwin. The internal discord that followed forced Baldwin to remain king, as only he was capable of uniting quarreling nobility. Baldwin again repelled Saladin in 1182, but leprosy rendered him blind and unable to walk or use his hands in 1183. He disinherited Guy and had Sibylla's son, Baldwin V, crowned co-king before having himself taken in a litter to lift Saladin's siege of Kerak. Baldwin failed to have Sibylla's marriage to Guy annulled and Guy's fief of Ascalon confiscated. In early 1185, he arranged for Raymond to rule as regent for Sibylla's son and died before 16 May.