Nader Shah Afshar (born Nader Qoli; Persian: نادرشاه افشار; 6 August 1698 or 22 October 1688 – 20 June 1747) was the founder of the Afsharid dynasty of Iran and one of the most powerful rulers in Iranian history, ruling as the emperor of Iran (Persia) from 1736 to 1747, when he was assassinated during a rebellion. He fought numerous campaigns throughout the Middle East, the Caucasus, Central Asia, and South Asia, emerging victorious from the battles of Herat, Mihmandust, Murche-Khort, Kirkuk, Yeghevārd, Khyber Pass, Karnal, and Kars. Nader belonged to the Turkoman Afshars, one of the seven Qizilbash tribes that helped the Safavid dynasty establish their power in Iran.

Nader rose to power during a period of chaos in Iran after a rebellion by the Hotaki Afghans had overthrown the weak emperor Soltan Hoseyn (r. 1694–1722), while the arch-enemy of the Safavids, the Ottoman Empire, as well as the Russian Empire, had seized Iranian territory for themselves. Nader reunited the Iranian realm and removed the invaders. He became so powerful that he decided to depose the last members of the Safavid dynasty, which had ruled Iran for over 200 years, and declared himself Shah in 1736. His numerous campaigns created a great empire that, at its maximum extent, briefly encompassed all or part of modern-day Afghanistan, Armenia, Azerbaijan, Bahrain, Georgia, India, Iran, Iraq, Turkey, Turkmenistan, Oman, Pakistan, Uzbekistan, the North Caucasus, and the Persian Gulf, but his military spending had a ruinous effect on the Iranian economy.

Nader Shah has been described as "the last great Asiatic military conqueror". He idolized Genghis Khan and Timur, the previous conquerors from Central Asia. He imitated their military prowess and, especially later in his reign, their cruelty. His victories during his campaigns briefly made him West Asia's most powerful sovereign, ruling over what was arguably the most powerful empire in the world.

Following his assassination in 1747, his empire quickly disintegrated, and Iran fell into a civil war. His grandson Shahrokh Shah was the last of his dynasty to rule, ultimately being deposed in 1796 by Agha Mohammad Khan Qajar, who crowned himself ruler of Qajar Iran the same year.

Nader belonged to the Turkoman Afshar tribe, which was one of the seven tribes of the Qizilbash who helped the Safavid dynasty establish their power in Iran. The Afshar tribe had originally lived in the Turkestan region, but during the 13th century they moved to the Azerbaijan region in northwestern Iran as a result of the expansion of the Mongol Empire.

Nader was from the semi-nomadic Qirqlu clan of the Afshars, which lived in the Khorasan region of northeastern Iran. They had either settled there during the reign of the first Safavid emperor, Ismail I (r. 1501–1524), or had been resettled by Shah Abbas I (r. 1588–1629) to fend off Uzbek attacks. Regardless, the Afshars' migration to Khorasan was already taking place by start of the 16th century.

The Afshar dialect is categorized either as a dialect of the Southern Oghuz group or a dialect of the Azerbaijani. As he was growing up, he must have swiftly learned Persian, which was the language of the cities and high culture. However, unless he was speaking to someone who spoke only Persian, he always preferred to communicate in Turkic. His knowledge of Arabic is not documented, but it seems doubtful given his lack of interest in literature and theology. Nader is known to have acquired reading and writing skills at some point in his life, probably later on.

Approximately three million people or more were nomadic or semi-nomadic pastoralists in Iran in the beginning of the 18th century, accounting for one-third of the country's population. Strong ties of kinship as well as customs of helping each other out with fights and finances kept their tribal groups united. Despite being partially or fully absorbed into the more urbanized Persian culture, many of them nevertheless identified culturally with the Turco-Mongol heritage that had been passed down from the era of Timur and Genghis Khan. The settled population was seen by the semi-nomads and nomads as inferior. Nader was part of this heritage, which the British academic Michael Axworthy calls "paradoxical".