Abu Abdallah 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-Shīʿī), was an Isma'ili missionary (dāʿī) active in Yemen and North Africa. He was successful in converting and unifying a large part of the Kutama Berber tribe, leading them on the conquest of Ifriqiya from 902 to 909 and the overthrowing of the Aghlabid dynasty. This ultimately led to the establishment of the Fatimid Caliphate in Ifriqiya under the Imam–caliph Abdullah al-Mahdi Billah. However, Abdullah al-Mahdi Billah quickly fell out with Abu Abdallah and had Abu Abdallah executed on 18 February 911.