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Abd Allah ibn Abi Quhafa (Arabic: عبد الله بن أبي قحافة, romanized: ʿAbd Allāh ibn ʾAbī Quḥāfa; c. 573 – 23 August 634), commonly known by the kunya Abu Bakr (Arabic: أبو بكر, romanized: ʾAbū Bakr), was the first caliph, ruling from 632 until his death in 634. A close companion and father-in-law of Muhammad, Abu Bakr is referred to with the honorific title al-Ṣiddīq (الصِّدِّيق, lit. the Veracious) by Sunni Muslims.

Born to Abu Quhafa and Umm al-Khayr of the Banu Taym, Abu Bakr was amongst the earliest converts to Islam and propagated dawah to the Mushrikites. He was considered the first Muslim missionary as several companions of Muhammad converted through Abu Bakr. He accompanied Muhammad on his migration to Medina and became one of the latter's bodyguards. Abu Bakr participated in all of Muhammad's campaigns and served as the first amir al-hajj in 631. In the absence of Muhammad, Abu Bakr led the prayers.

Following Muhammad's death in 632, Abu Bakr succeeded the leadership of the Muslim community as the first caliph, being elected at Saqifa. His election was contested by a number of rebellious tribal leaders. During his reign, he overcame a number of uprisings, collectively known as the Ridda wars, as a result of which he was able to consolidate and expand the rule of the Muslim state over the entire Arabian Peninsula. He also commanded the initial incursions into the neighbouring Sasanian and Byzantine empires, which in the years following his death, would eventually result in the Muslim conquests of Persia and the Levant. Apart from politics, Abu Bakr is also credited for the compilation of the Quran, of which he had a personal caliphal codex. Prior to dying in August 634, Abu Bakr nominated Umar (r. 634–644) as his successor. Along with Muhammad, Abu Bakr is buried in the Green Dome at the Al-Masjid an-Nabawi in Medina, the second holiest site in Islam. He died of illness after a reign of 2 years, 2 months and 14 days, the only Rashidun caliph to die of natural causes.

Though Abu Bakr's reign was short, it included successful invasions of the two most powerful empires of the time, the Sassanian Empire and the Byzantine Empire. He set in motion a historical trajectory that in a few decades would lead to one of the largest empires in history. His victory over the local rebel Arab forces is a significant part of Islamic history. Sunni Muslims revere Abu Bakr as the first of the rightly-guided caliphs and the greatest individual after the prophets and messengers. Shia tradition considers Abu Bakr an usurper of the caliphate and an enemy of the ahl al-bayt.