Abd Allah ibn Saba

Abd Allah ibn Saba () was an Arab Jewish religious leader in the 7th-century. His followers were known as Saba'iyya.
Ghulat career.
Abd Allah ibn Saba is considered the first ghulat (extremist). He was the first one to declare faith in the Imamate of Ali. After Ali’s death, he is said to maintain this idea that "a devil in ʿAli’s appearance had been murdered" and ʿAli had ascended to heaven and that his occultation (rajʿa) was imminent. Saba probably invented the concept of ghayba and return.
Heinz Halm records him as a representative of a Ghulat group from the city of Seleucia-Ctesiphon ("al-Madā'in") who came to see ‘Alī in Kūfah. When Saba proclaimed divinity, then ‘Alī denied this angrily and exiled him back to Seleucia-Ctesiphon.
Roles in Uthman’s assassination.
Tabari and Sayf ibn Umar record Abd Allah ibn Saba from playing any major role in the political events that led to Uthman's killing. He and his followers are said to be the ones who enticed the Egyptians against Uthman on the ground of Ali's special right of succession, and participated in further instigation at later conflicts.
Legacy.
There is a favorable Shia quote that formed around the figure of Abdullah ibn Saba. The story of Saba has also been used by Shia factions to both attack and defend extreme Shia groups. In an non-authentic Shia source, Abd Allah ibn Saba was cursed by Ja'far al-Sadiq.
Criticism.
Jews view Saba negatively and historical Jewish sources regarded him as an apostate from Judaism. Sunni Muslims view Saba as a ghulat seeking to corrupt the message of Islam from by introducing proto-Shia beliefs. Since Saba used to hate Abu Bakr, Umar and Uthman, Sunni Muslims view him negatively and curse him. Sa'd ibn Abdullah al-Ash'ari al-Qummi reported in al-Maqaalaat wal-Firaq p. 20: