Eustace III, Count of Boulogne, was a nobleman from the 12th century, known for his role in the Crusades. He was born around 1096 and was the son of Eustace II, Count of Boulogne. Eustace III became the count after his father's death and was involved in various military campaigns, including the First Crusade. Eustace III was also notable for his connections to the English crown, as he was the brother-in-law of King Stephen of England. His lineage and alliances played a significant role in the political landscape of medieval Europe, particularly in the regions of Flanders and Normandy.