Iran, also known as Persia, officially the Islamic Republic of Iran, is a country in Western Asia. With over 81 million inhabitants, Iran is the world's 18th-most-populous country. Comprising a land area of 1,648,195 km², it is the second-largest country in the Middle East and the 17th-largest in the world.
Iran is home to one of the world's oldest civilizations, beginning with the formation of the Elamite kingdoms in the fourth millennium BCE. It was first unified by the Iranian Medes in the seventh century BCE, reaching its greatest territorial size in the sixth century BCE, when Cyrus the Great founded the Achaemenid Empire, which stretched from Eastern Europe to the Indus Valley, becoming one of the largest empires in history. The Iranian realm fell to Alexander the Great in the fourth century BCE and was divided into several Hellenistic states. An Iranian rebellion culminated in the establishment of the Parthian Empire, which was succeeded in the third century CE by the Sasanian Empire, a leading world power for the next four centuries.
The sovereign state of Iran is a founding member of the UN, ECO, NAM, OIC, and OPEC. It is a major regional and middle power, and its large reserves of fossil fuels – which include the world's largest natural gas supply and the fourth-largest proven oil reserves – exert considerable influence in international energy security and the world economy.
The country's rich cultural legacy is reflected in part by it is 22 UNESCO World Heritage Sites, the third-largest number in Asia and eleventh-largest in the world. Iran is a multicultural country comprising numerous ethnic and linguistic groups, the largest being Persians (61%), Azeris (16%), Kurds (10%), and Lurs (6%).