al-Mahdi - Khalīfah of al-Khilāfatu al-‘Abbāsīyah from 6. Oct 775 to 24 July 785
Abu Abdallah Muhammad ibn Abdallah al-Mansur (Arabic: أبو عبد الله محمد بن عبد الله المنصور‎‎), better known by his regnal name al-Mahdi (المهدي, "He who is guided by God"), was the third Abbasid Caliph who reigned from 775 to his death in 785. He succeeded his father, al-Mansur.

Al-Mahdi reigned for ten years. He imprisoned his most trusted vizier Ya'qub ibn Dawud, and in the year 167 AH/ 783 AD, al-Mahdi instituted an official inquisition which led to the execution of alleged Zindiq (heretics).
al-Mahdi
Caliph al-Mahdi "He who is guided by God" of the Abbasid Caliphate

Epithet: al-Mahdi ("He who is guided by God")

(1) al-Mahdi 780 AD
Obverse: Margin: بسم الله ضرب هذا الدرهم بمدينة جى سنة اثنين و ستين و مئة Center: لا الاه الا الله وحده لا شريك له
Reverse: Margin: محمد رسول الله ارسله بالهدى و دين الحق ليظهره على الدين كله ولو كره المشركون Center: محمد رسول الله صلى الله عليه و سلم الخليفة المهدى يحيى
Ref: A.215.1