Eustace I of Boulogne was a nobleman from the 11th century, known for his role as the Count of Boulogne. He was born around 1020 and was a significant figure in the early medieval period, particularly in the region of Flanders. Eustace was a supporter of the Norman Conquest and participated in the campaigns led by William the Conqueror. Eustace I was also the father of Eustace II of Boulogne, who continued the family's legacy. His lineage played a crucial role in the political landscape of Northern France and England during the medieval era, influencing the relationships between various noble houses.