Ali Hosseini Khamenei (আলী খামেনেয়ী) is an Iranian cleric and politician who has served as the second supreme leader of Iran since 1989. His tenure as supreme leader, spanning over 35 years, makes him the longest-serving head of state in the Middle East and the second-longest-serving Iranian leader of the 20th and 21st centuries, after Shah Mohammad Reza Pahlavi.

Born in Mashhad to the Khamenei family originating from the town of Khamaneh, East Azerbaijan, Ali Khamenei studied at a hawza in his hometown, later settling in Qom in 1958 where he attended the classes of Ruhollah Khomeini. Khamenei became involved in opposition to Mohammad Reza Pahlavi, the shah of Iran, and was arrested six times before being exiled for three years by the Shah's regime. Khamenei was a mainstream figure in the Iranian Revolution (1978–1979), and upon its success, held many posts in the newly-established Islamic Republic of Iran. In the aftermath of the revolution, he was the target of an attempted assassination that paralysed his right arm. Khamenei served as the third president of Iran from 1981 to 1989 during the Iran–Iraq War, when he also developed close ties the Islamic Revolutionary Guard Corps (IRGC). After the death of Khomeini in 1989, Khamenei was elected supreme leader by the Assembly of Experts.

Ali Khamenei was born on 19 April 1939 to Javad Khamenei, an Alim and Mujtahid born in Najaf, Iraq, and Khadijeh Mirdamadi (daughter of Hashem Mirdamadi) in Mashhad, Khamenei is the second of eight children. Two of his brothers are also clerics; his younger brother, Hadi Khamenei, is a newspaper editor and cleric. His elder sister Fatemeh Hosseini Khamenei died in 2015, aged 89. His father was an ethnic Azerbaijani from Khamaneh, while his mother was an ethnic Persian from Yazd. Some of his ancestors are from Tafresh in today's Markazi Province and migrated from their original home in Tafresh to Khamaneh near Tabriz.

Khamenei's ancestor was Sayyid Hossein Tafreshi, a descendant of the Aftasi Sayyids supposedly reaching to Sultan ul-Ulama Ahmad, known as Sultan Sayyid, a grandchild of the fourth Shia Imam, Ali al-Sajjad.

Khamenei's education began at the age of four, by learning the Quran at Maktab; he spent his basic and advanced levels of seminary studies at the hawza of Mashhad, under mentors such as Sheikh Hashem Qazvini and Ayatollah Milani. Then, he went to Najaf in 1957, but soon returned to Mashhad due to his father's unwillingness to let him stay there. In 1958, he settled in Qom where he attended the classes of Seyyed Hossein Borujerdi and Ruhollah Khomeini. Like many other politically active clerics at the time, Khamenei was far more involved with politics than religious scholarship.

According to his official website, Khamenei was arrested six times before being exiled for three years during the reign of Mohammad Reza Pahlavi. Khamenei was a key figure in the Iranian Revolution in Iran and a close confidant of Ruhollah Khomeini. Since the founding of the Islamic Republic, Khamenei has held many government posts. Khamenei has been head of the servants of Astan Quds Razavi since 14 April 1979. Muhammad Sahimi asserted that his political career began after the Iranian Revolution, when the former President of Iran, Akbar Hashemi Rafsanjani, then a confidant of Khomeini, brought Khamenei into Khomeini's inner circle. Later on, Hassan Rouhani, then a member of Parliament, arranged for Khamenei to get his first major post in the provisional revolutionary government as deputy defense minister.

In 1980 after the resignation of Hussein-Ali Montazeri from the position, Ruhollah Khomeini appointed Ali Khamenei to the position of Tehran's Friday Prayers Imam. Khamenei was briefly the Vice Minister of National Defence from late July to 6 November 1979 and as a supervisor of the Islamic Revolutionary Guards. He also served on the battlefield as a representative of the Iranian Parliament's Defense Commission.

Khamenei narrowly escaped assassination by the Mujahedin-e Khalq when a bomb, concealed in a tape recorder, exploded beside him. On 27 June 1981, while Khamenei had returned from the frontline, he went to the Aboozar Mosque according to his Saturday's schedule. After the first prayer, he lectured to worshippers who had written their questions on paper. Meanwhile, a young man who pressed a button put a tape recorder accompanied by papers on the desk in front of Khamenei. After a minute the recorder began whistling, then suddenly exploded. "A gift of Furqan Group to the Islamic Republic" was written on the inner wall of the tape recorder. Khamenei's treatment took several months and his arm, vocal cords and lungs were seriously injured. He was permanently injured, losing the use of his right arm.