Simeon I of Bulgaria
Leo was apparently a relative to the ruling Macedonian dynasty, and a brother-in-law of the famed diplomat Leo Choirosphaktes. In 917, he was governor ("strategos") of the theme of Dyrrhachium, and was sent to the Serbian ruler Petar Gojniković (r. 892–917) to persuade him to attack Simeon I of Bulgaria (r. 893–927), with whom the Byzantines were at war. Leo was successful, but the Serbian attack failed and Petar was taken captive. From the "De Administrando Imperio" of Emperor Constantine VII Porphyrogennetos (r. 913–959), it is also known that Leo was later promoted from his rank of "protospatharios" to that of "magistros", and became Logothete of the Drome (foreign minister).