Abu Bakr was a friend and father-in-law to Muhammad, the founder of Islam, and he was an influential figure in early Islamic history. Abu Bakr was one of the first Muslims, and he eventually became the first caliph, or successor to Muhammad. Abu Bakr used his wealth, influence and time to spread Islam, and he later set the stage for Islam's explosive expansion.

An Influential Person

Before the advent of Islam, Abu Bakr was one of Mecca's wealthiest merchants. He also held a political office responsible for awarding "blood money" -- the price paid to a family after one its members had been murdered. Much of Abu Bakr's reputation in the community stemmed from his honesty, trustworthiness and fairness in judging disputes. Three years after the death of Khadija, Muhammad's first wife, Aisha and Muhammad were married. This strengthened Abu Bakr's influence, and Aisha eventually became Muhammad's favorite wife and earned the title "Mother of the Believers."

Financing the Faith

Muhammad said that Abu Bakr, above everyone else, favored him with his companionship and wealth. Abu Bakr put his money where his mouth was, donating all he could to the cause of Islam. Abu Bakr financed the Hijra, the Muslims' journey from Mecca to Medina in the year 622. He also bought land for mosques, funding the famous Mosque of the Prophet in Medina, and he funded Muslim military expeditions.

Ascension to Caliph Amid Controversy

When Muhammad died in 632, Abu Bakr became the caliph, or successor to Muhammad. This decision is still controversial, and it fuels the split between the Sunni and Shia sects of Islam. The Sunni believe Abu Bakr was the correct choice, but the Shia believe Ali -- Muhammad's cousin and son-in-law -- should have been the first caliph. Sunnis believe Abu Bakr was chosen because there was no clear successor, while Shias believe Muhammad had specifically appointed Ali as his successor.

Instant Rebellion

In pre-Islamic Arabia, the death of a tribe's leader ended any alliances with that tribe, so many of the Bedouin tribes refused to accept the authority of Abu Bakr after Muhammad's death in 632. Abu Bakr was able to suppress these revolts, which are known as the Ridda Wars or the Wars of Apostasy, by the year 633. Abu Bakr united the Arabian Peninsula under Islam and created a new form of allegiance -- an allegiance to Islam rather than to a tribe or a leader.

Looking Beyond Arabia

With Arabia unified, Abu Bakr looked north with a desire to expand at the expense of the two great powers at the time -- the Byzantine Empire and the Sassanid Empire. Before his death in 634, Abu Bakr declared the Muslims' hostile intentions toward the Byzantines and the Sassanids, and he declared a jihad, or holy war, against the Byzantines in Syria. These actions set the table for Muslim expansion, and within 10 years Muslims ruled a territory stretching from North Africa to Persia.