Baha'i faith or Bahaism as a religion had as its background two earlier and much different movements in nineteenth-century Shi'ite Shaikhism

Baha'i faith or Bahaism as a religion had as its background two earlier and much different movements in nineteenth-century Shiʿite Shaikhism (following Shaikh Aḥmad Aḥsāʾī) and Babism. Shaikhism centered on theosophical doctrines and believed that a perfect Shiʿite existed on earth at all times, and many Shaikhis (as well as other Shiʿites) expected the return of the hidden Twelfth Imam in 1260/1844. Shaikhis in particular joined the messianic Babi movement of the 1840s, which shook Iran as Sayyed ʿAlī-Moḥammad Šīrāzī proclaimed himself, first the bāb or “gate” of the Twelfth Imam, and then the return of the imam himself. As the new creed spread, violence broke out between Shiʿites and Babis, ending when Qajar government troops intervened to besiege and massacre the Babis. The government executed the Bāb in 1850. Some Babi leaders in Tehran plotted, in revenge, the death of Nāṣer-al-Dīn Shah, but the assassination failed and large numbers of suspected Babis were tortured and killed.

(Encyclopaedia Iranica Online)

https://referenceworks.brillonline.com/entries/encyclopaedia-iranica-online/bahai-faith-or-bahaism-COM_6391