Abu Bakr Abdullah ibn Uthman Abi Quhafa (Arabic: أَبُو بَكْرٍ عَبْدُ ٱللهِ إبْنِ أَبِي قُحَافَةَ, romanized: Abū Bakr ʿAbd Allāh ibn ʿAbī Quḥāfa; 27 October 573 – 23 August 634) was the senior companion and was, through his daughter Aisha, a father-in-law of the Islamic prophet Muhammad, as well as the first Caliph of the Rashidun Caliphate. He is known with the honorific title "al-Siddiq" by Sunni Muslims.

Abu Bakr was born in 573 CE to Abu Quhafa and Umm Khayr. He belonged to the tribe of Banu Taym. In the Age of Ignorance, he was a monotheist and condemned idol-worshipping. As a wealthy trader, Abu Bakr used to free slaves. Following his conversion to Islam in 610, Abu Bakr served as a close aide to Muhammad, who bestowed on him the title "al-Siddiq" ('the Truthful/Righteous'). The former took part in almost all battles under the Islamic prophet. He extensively contributed his wealth in support of Muhammad's work and among Muhammad's closest companions. He also accompanied Muhammad on his migration to Medina. By the invitations of Abu Bakr, many prominent Sahabis became Muslims. He remained the closest advisor to Muhammad, being present at almost all his military conflicts. In the absence of Muhammad, Abu Bakr led the prayers and expeditions.

Following Muhammad's death in 632, Abu Bakr succeeded the leadership of the Muslim community as the first Rashidun Caliph. His election was opposed by a large number of rebellious tribal leaders, who had apostatized from Islam. 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 Sassanian 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. Abu Bakr nominated his principal adviser Umar (r. 634–644) as his successor before dying in August 634. 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 the period of his caliphate was short, it included successful invasions of the two most powerful empires of the time, a remarkable achievement in its own right. 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. Abu Bakr is widely honored among Muslims.