The Rashidun Caliphs (Rightly Guided Caliphs; Arabic: الخلفاء الراشدون‎ al-Khulafāʾu ar-Rāshidūn), often simply called, collectively, "the Rashidun", is a term used in Sunni Islam to refer to the 30-year reign of the first four caliphs (successors) following the death of the Islamic prophet Muhammad, namely: Abu Bakr, Umar, Uthman ibn Affan, and Ali of the Rashidun Caliphate, the first caliphate. The caliphate of Hasan ibn Ali is sometimes also considered to be Rashidun as well but since it was merely a six month period it is not mentioned categorically.