Abū Jaʿfar Hārūn ibn Muḥammad, better known by his regnal name al-Wāthiq bi-llāh, was an Abbasid caliph who reigned from 842 until 847 CE.

Abū Isḥāq Muḥammad ibn Hārūn al-Rashīd, better known by his regnal name al-Muʿtaṣim biʾllāh, was the eighth Abbasid caliph, ruling from 833 until his death in 842. A younger son of Caliph Harun al-Rashid, he rose to prominence through his formation of a private army composed predominantly of Turkic slave-soldiers. This proved useful to his half-brother, Caliph al-Ma'mun, who employed al-Mu'tasim and his Turkish guard to counterbalance other powerful interest groups in the state, as well as employing them in campaigns against rebels and the Byzantine Empire. When al-Ma'mun died unexpectedly on campaign in August 833, al-Mu'tasim was thus well placed to succeed him, overriding the claims of al-Ma'mun's son al-Abbas.