Baldwin of Boulogne (died 1118), count of Edessa (1098—1100), and first king of Jerusalem (1100—1118), was the brother of Godfrey of Bouillon, son of Eustace II of Boulogne.
As the younger brother of Godfrey, Baldwin was originally a clerk-in-orders, and held several church properties. In 1096 he joined the First Crusade, and accompanied his brother Godfrey as far as Heraclea in Asia Minor. When Tancred left the main body of the crusaders at Heraclea and marched into Cilicia, Baldwin followed him, partly in jealousy, and partly from the same politics that motivated Tancred. In September of 1097 he took Tarsus from Tancred, and installed his own garrison in the city. After rejoining the main army at Marash, he received an invitation from an Armenian named Pakrad, and moved eastwards towards the Euphrates where he occupied Tell-bashir. Another invitation came from Thoros of Edessa, where Baldwin was adopted as Thoros' son and successor. When Thoros was assassinated in March of 1098, Baldwin became the first count of Edessa, although it is unknown if he played any role in the assassination. He ruled the county until 1100, marrying an Armenian wife, and acting as an ambassador between the crusaders and Armenians.
During these two years he captured Samosata and Seruj (Sarorgia) from the Muslims, and defeated a conspiracy by some of his Armenian subjects in 1098. At the end of 1099 he visited Jerusalem along with Bohemund I of Antioch, but he returned to Edessa in January 1100. After Godfrey's death in 1100 he was invited to Jerusalem by the supporters of a secular monarchy, and was crowned as the first king of Jerusalem on Christmas Day, 1100, by Dagobert of Pisa, the Patriarch, who would have preferred to turn the kingdom into a theocracy. In the spring of 1101 Baldwin had Dagobert suspended by a papal legate, while later in the year the two disagreed on the question of the contribution to be made by the patriarch towards the defence of the Holy Land. The struggle ended in the deposition of Dagobert in 1102.
After Baldwin had secured the supremacy of the monarchy in Jerusalem, he extended the influence of the kingdom over the other cities that had not yet been captured. He was helped by an alliance with the Italian trading towns, especially Genoa, which supplied siege engines and naval support in return for the trading quarters in each of the conquered cities. Arsuf and Caesarea were captured in 1101, Acre in 1104, and Beirut and Sidon in 1110 (the latter with the aid of the Venetians and Norwegians).
Meanwhile Baldwin defeated invasions from Egypt in 1102, 1103, and 1105, and from 1115 to 1118 he captured territory from Egypt, gaining access to the Red Sea and building the fortress of Montreal. In the north he became the nominal suzerain of the County of Tripoli, the Principality of Antioch and the County of Edessa, and helped them defend against Muslim invasions from Syria, especially Mawdud and Aksunk-ur of Mosul. He died in 1118, after an expedition to Egypt, during which he captured Farama, and, as 17th century historian Thomas Fuller remarked, "caught many fish, and his death in eating them."
The Historia Hierosolymitana of Fulcher of Chartres, who had accompanied Baldwin to Edessa as Baldwin's chaplain, and had lived in Jerusalem during his reign, is the primary source for Baldwin's career.