1. First caliph was Abu Bakr, Muhammad's father-in-law and close friend
2. Abu Bakr died about two years after he was elected and was succeeded in 634 by Caliph Umar, another father-in-law of Muhammad
3. When Umar was assassinated six years after being named caliph, Uthman, Muhammad's son-in-law, took the role
4. Uthman was also killed, and Ali, Muhammad's cousin and son-in-law, was selected as the next caliph