Reviewing and/or perusing the Ahadith and Islamic History on the above issue, one may safely say that the 12 Caliphs are as follows:--
Abu Bakr as-Sadiq (632-634), Umar al-Faruq (634-644), Uthman Ibn Affan (644-656), Ali Ibn Abi Talib (656-661),
Al-Hassan Ibn Ali (661-661), Mu'awiyya Ibn Sufyan (661-680), Abdullah Ibn az-Zubair (683-692), Umar Ibn Abdul'aziz (717-720)
Al-Muhtadi Bi'amrillah (869-870), At-Taahir Billah (1225-1226), and Shehu Uthman Ibn Fodio (1803-1817)
Each of these mean, may Allah be pleased with them, were responsible for establishing Justice, Equity and Reviving the religion of Islam.