Uthman ibn Affan (Arabic: عثمان بن عفان, romanized: ʿUthmān bin ʿAffān; c. 573 or 576 – 17 June 656 CE), also spelled by Colloquial Arabic, Turkish and Persian rendering Osman, was a second cousin, son-in-law and notable companion of the Islamic prophet Muhammad, as well as the third of the Rāshidun, or "Rightly Guided Caliphs". Born into a prominent Meccan clan, Banu Umayya of the Quraysh tribe, he played a major role in early Islamic history, and is known for having ordered the compilation of the standard version of the Quran. When Caliph Umar ibn al-Khattab died in office aged 60/61 years, Uthman, aged 68–71 years, succeeded him and was the oldest to rule as Caliph.

Under Uthman's leadership, the Islamic empire expanded into Fars (present-day Iran) in 650, and some areas of Khorāsān (present-day Afghanistan) in 651. The conquest of Armenia had begun by the 640s. His reign also saw widespread protests and unrest that eventually led to armed revolt and his assassination.

Uthman was married to Ruqayya, and upon her death, married Umm Kulthum. Both his wives having been elder daughters of Muhammad and Khadija earned him the honorific title Dhū al-Nurayn ("The Possessor of Two Lights"). Thus, he was also brother-in-law of the fourth Rāshidun Caliph Ali whose own wife, Fātimah, was Muhammad's youngest daughter.