Zayd ibn Ali
In the context of the Shi'a Muslim belief in spiritual leadership or Imamate, Zaydis believe that the leader of the Ummah or Muslim community must be "Fatimids": descendants of Muhammad through his only surviving daughter Fatimah, whose sons were Hasan ibn ʻAlī and Husayn ibn ʻAlī. These Shi'a called themselves Zaydi so they could differentiate themselves from other Shi'is who refused to take up arms with Zayd ibn Ali.