al-Qasim al-Rassi

al-Qasim ibn Ibrahim al-Rassi (born c. 169/170 AH, c. 785 CE; died 246 or, by some reports, 243 AH, 860 CE) was an early religious scholar of the Hijaz and one of the formative theologians of the Zaydi branch of Shia Islam. The Zaydis — sometimes called "Fivers" — count him among their imams (recognized religious-political leaders). Through his descendants he gave his name to the Rassid line that later ruled in Yemen.

He was a descendant of al-Hasan, grandson of the Prophet Muhammad, and grew up in Medina, where reports say he studied under a teacher connected to the school of the jurist Malik ibn Anas. He developed a rationalist theology close to that of the Mu'tazila — a school that stressed God's absolute unity (tawhid) and justice, denied any likeness between God and creation, and affirmed human free will. Zaydi tradition honors him with titles such as "Star of the Family of the Prophet."

Sometime before 815 CE he settled in Egypt, probably at Fustat, where he is reported to have studied Christian and Jewish writings and composed polemical treatises, including a refutation of Christian doctrine and a reply to a Manichaean text. Around 827 he withdrew to a village near the Wadi al-Rass, southwest of Medina — the source of his nisba "al-Rassi" — where he taught and wrote until his death. Many later figures present his thought as foundational, though the details of his life rest largely on Zaydi tradition.