Muhammad's successors were call caliphs. From the beginning, there was disagreement about what characteristics would qualify someone to be a caliph. The four "Rightly Guided Caliphs" were in power in successive years from 632 to 661. The two major divisions in Islam are the Shia and Sunni Muslims. One of the major differences between these two movements was over how the successors to Muhammad would be determined. A third movement in Islam is known as Sufi.