Who became the leader of Islam right after the prophet Mohammad?
Shortly after Mohammed's death, Mohammed's father-in-law Abu Bakr (circa 573- 634) became the Caliph of the recently created Islamic state and united all the tribes of Arabia under Islamic rule. He and the next three caliphs would become known as the Four Rightly Guided Caliphs and were highly successful in spreading Islam from Persia through northern Africa. The third caliph, Ali ibn Abi Talib (598- 661) would come from a different tribe than Mohammed and the former two caliphs, which led to a major division within Islam, between the Sunnis and Shiites, that continues to the present. John Esposito in The Oxford History of Islam gives an excellent history of Islam.