Hasan, who assumed the regnal name al-Dāʿī ilaʾl-Ḥaqq ("He who summons to the Truth"), was recognized as emir by a part of the local population, and even secured the allegiance of the Justanid king of Daylam, Vahsudan ibn Marzuban.

[1][4][5] Despite the rapid success of the rebellion, Hasan's reign was troubled due to repeated invasions, and he was several times forced to seek refuge in Daylam.

Nevertheless, Ya'qub's army soon became bogged down by torrential rainfall and suffered many casualties to disease in the unaccustomed subtropical climate of Tabaristan, forcing him to withdraw from the region shortly after.

[1][5] Historians praised him as a just and equitable ruler,[6] but outside the early strongholds of Ruyan and Kalar, the initial enthusiasm for his rule seems to have waned quickly among the broad populace of Tabaristan and Gurgan.

[10] The Orientalist Frants Buhl assesses Hasan's character thus: he "possessed rare energy and the capacity for stubborn resistance, was a sincerely religious man, well educated, and a patron of letters".