The Kingdom of Jerusalem was considered to be a Crusader state from 1098 to 1291. It covered the regions that are now Israel, Palestine, the West Bank, and the Gaza Strip.
The kingdom was established after the First Crusade (the series of religious wars from 1096 - 1099 directed by the Latin Church during the medieval period). The city was conquered in 1099 and Latin Catholic leaders ensured that Jerusalem had a supreme leader who was anointed as king.
The rulers of the Kingdom of Jerusalem during the time period of 1098 to 1291 were primarily Frankish kings of French origin. Baldwin IV was one of them. He was from the House of Anjou, a peerage of France.
Baldwin's father was king of Jerusalem before him and his mother was a Frankish noblewoman. Baldwin only reigned for a short while after his father died and he succeeded to the throne.
During his short life, he was afflicted with leprosy which he first faced when he was a child. The disease eventually left his face disfigured and he became blind. He was also unable to use his hands and feet.
Despite his short life (he would die at the age of 24), Baldwin protected his kingdom against the Ayyubid Muslim ruler, Saladin.
Baldwin fought against Saladin in the Battle of Montgisard. He was only 16 years old at the time but he led an outnumbered Christian army against the Ayyubid ruler, Saladin. Baldwin was brave and fought with his army even though he was suffering from an aggressive form of leprosy.
It is reported that he had bandaged his arms to cover his sores and he needed help to get off his horse. But he carried a relic of the True Cross to battle with him and prayed to God.
Saladin was defeated and his army fled back to Cairo, Egypt. (A two-year truce was arranged but Saladin would later capture Aleppo and completely encircle Jerusalem.)
In the meantime, Baldwin continued fighting battles to protect Jerusalem until he could no longer walk. Before he died at the age of 24, he appointed his nephew to become King Baldwin V.