Al-Husayn ibn Ahmad ibn Muhammad ibn Zakariyya, better known as Abu Abdallah al-Shi'i (Arabic: ابو عبد الله الشيعي, romanized: Abū ʿAbd Allāh ash-Shi'ī), was an Isma'ili missionary (dāʿī) active in Yemen and North Africa, mainly among the Kutama Berbers. He was successful in converting and unifying a large part of the Kutama, leading them to the conquest of Ifriqiya in 902–909 and the overthrow of the Aghlabid dynasty. This allowed the establishment of the Fatimid Caliphate in Ifriqiya under the imam–caliph Abdullah al-Mahdi Billah, but the latter quickly fell out with Abu Abdallah, and had him executed on 28 February 911.