The four Rightly Guided Caliphs (Khulfa-Rashideen) are: Abu Bakr As-Siddiq, Umar ibn Al-Khattab, Uthman ibn Affan (Usman Ghani), and Ali ibn Abi Talib. Abdullah bin Abdul Aziz was a modern Saudi King (2005-2015), not one of the four Rashidun Caliphs who succeeded Prophet Muhammad.