Simeon I of Bulgaria
Nicholas Mystikos, ecumenical patriarch of Constantinople, was the principal regent until March 914. He was displaced by Zoe Karbonopsina, mother of the young emperor. Zoe reigned with the support of influential general Leo Phocas until 919. However, Leo led the Byzantine army into a series of lost battles against Simeon I of Bulgaria in one campaign of the Byzantine-Bulgarian Wars. This strengthened the opposition to the regent and her favorite general.