 Appointed to the "kavhan" office under Omurtag, Isbul was a regent or co-ruler of the underage Malamir and his successor Presian.Under Malamir and Presian, Isbul headed Bulgaria's successful campaigns against the Byzantines in southern Thrace and Macedonia, which led to a significant territorial expansion of the Bulgarian realm.As a co-ruler of Malamir, Isbul also financed the construction of a water conduit in the capital Pliska.