High Quality Content by WIKIPEDIA articles! Isbul (Bulgarian: Исбул) (fl. 820s–830s) was the kavhan, or first minister, of the First Bulgarian Empire during the reigns of Omurtag, Malamir and Presian I. Appointed to the kavhan office under Omurtag, Isbul was a regent or co-ruler of the underage Malamir and his successor Presian.