Cyriacus II of Constantinople was a 6th-century prelate who served as the Ecumenical Patriarch of Constantinople from 596 until 606. Before ascending to this high position, he worked as a presbyter and as the steward of the great church in his home city. His leadership was characterized by a firm adherence to the title of ecumenical bishop, a practice that led to significant theological and political friction with Pope Gregory I, who viewed the claim as a threat to church unity.