Abdullah ibn Abi Qhuhafah (573-23 August 634), also known as Abu Bakr, was a sahabi (companion) and father-in-law of Muhammad. He was the first ruler of the Rashidun Caliphate, reigning from 632 to 634 - he was therefore the first Caliph. He was succeeded by Umar.
Biography
Sahabah
Abdullah ibn Abi Qhuhafah (abu Bakr) was born in 573 CE in Mecca to the Banu Taym clan of the Quraysh tribe, and he grew up with a fondness for camels. When he was ten, he met Muhammad while traveling with a merchant convoy to Byzantine Empire-ruled Syria. He became a cloth merchant like his father, and traveled to Syria, Yemen, and elsewhere. When he returned from Yemen, he found out that the people of Mecca said that Muhammad declared himself the messenger of God (Allah). Abu Bakr was around the 50th man to embrace the new religion of Islam, with the first man being Ali. He divorced his wife Qutaylah bint Abd-al-Uzza when she did not embrace Islam, while his other wife Um Raman did. His conversion inspired future third Caliph Uthman ibn Affan and future generals Al-Zubayr, Abdur Rahman bin Awf, Sa'd ibn Abi Waqqas, and Abu Ubaidah ibn al-Jarrah to also convert to Islam from paganism. He prayed in secret, as the Quraysh persecuted Muslims. In 615 he fled to Abyssinia (Ethiopia), but in 617 he returned to Mecca. In 624 he defended Muhammad's tent during the Battle of Badr against the Quraysh, and also took part in the 625 defeat at the Battle of Uhud. Also in 625, he fought the Jewish Banu Nadir tribe and won the Battle of Khaybar against them. He guarded a belt of "the Trench" in his sector during the 627 AD Battle of the Trench in the surrounding perimeter of Mecca with bravery, helping in the victory. He later commanded troops in expeditions against the Byzantine Empire, and led an expedition against seven houses of polytheists in Nejd, killing many pagans.
First caliph
Caliph Abu Bakr
After Muhammad's death in 632, a split between the Ansar converts of Medina and the Muhajiurn Meccan immigrants threatened to divide the Ummah, so Abu Bakr, Umar, and Abu Ubaidah ibn al-Jarrah prevented the Ansar from making a premature decision. Abu Bakr was elected as the first Caliph of the new Rashidun Caliphate, the Islamic state in the Arabian Peninsula that Muhammad had worked to found before he died. He crushed Arab rebels in the Ridda Wars, and Khalid ibn al-Walid led his armies in the victories such as the Battle of Yamama. After Yamama, in which many of the Muslims who memorized the Quran were killed, he decided to preserve the writings by putting them down in written format. He sent Khalid ibn al-Walid to conquer spice-rich Iraq from the Sassanid Empire of Persia, and Khalid won the Battle of Chains, the Battle of River, the Battle of Walaja, and the Battle of Ullais in 633. After the December 633 Battle of Firaz, the Muslim conquest of Iraq ended. In 634, Khalid ibn al-Walid took command of an army of Muslim troops sent to conquer Syria from the Byzantines, and Abu Bakr personally oversaw the great campaign that defeated the Byzantines. Abu Bakr died during the Siege of Damascus, and Umar succeeded him as Caliph.