Abu Bakr (Arabic: أَبُو بَكْرٍ, romanized: Abū Bakr; c. 27 October 573 – 23 August 634) was the founder and first caliph of the Rashidun Caliphate ruling from 632 until his death in 634 which he was the first caliphate. He was the most prominent companion, closest advisor and a father-in-law of the Islamic prophet Muhammad (c. 570–632).

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. He was an early friend of Muhammad and often used to accompany him on trading in Syria. After Muhammad's invitation of Islam, Abu Bakr became one of the first Muslims. He extensively contributed his wealth in support of Muhammad's work and 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, being elected at Saqifah. 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 Islamic state over the entire Arabian Peninsula. He also commanded the initial incursions into the neighboring Sassanian and Byzantine empires, which in the years following his death, would eventually result in the Muslim conquests of Persia and the Levant. Abu Bakr also had an essential role in the compilation of the Quran during his reign. The first finished codex of the Quran was kept with Abu Bakr. All modern versions of the Quran are derived from Abu Bakr's codex.Abu Bakr's caliphate lasted for only two years, ending with his death after an illness in 634. On his deathbed, he dictated his last testament to Uthman ibn Affan, in which he appointed Umar ibn al-Khattab as his successor. Abu Bakr's ghusl was performed by Ali ibn Abi Talib and the funeral prayer was performed by Umar. 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.

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.