Umar
At first, Umar opposed Muhammad. After his conversion to Islam in 616, Umar became the first Muslim to openly pray at the Kaaba. Umar fought in almost all battles under Muhammad. After Muhammad's death in June 632, Umar pledged allegiance to Abu Bakr () as the first caliph. Umar served as the closest adviser to the Bakr until August 634. It was then that the dying Abu Bakr made Umar his successor.