 In order to accede to that position, Isbul must have belonged to the Kavhan family, which is indirectly evidenced by his Bulgar name.Historian Plamen Pavlov theorises that Isbul may have begun his career under the ruler Krum (r. 803–814), and by the time of Krum's son Omurtag (r. 815–831), Isbul was already an influential noble.As he is referred to as a "kavhan" and regent of the next ruler, Malamir (r. 831–836), it is conjectured that he had been appointed to the office at some point during Omurtag's rule.