Supreme Leader Ayatollah Ali Khamenei was born in Mashhad, Iran in 1939. He studied in Qom under prominent Shia scholars, including the Islamic Republic’s founder and former Supreme Leader Ayatollah Ruhollah Khomeini. Khamenei became one of Khomeini’s top advisors. After the 1979 Islamic Revolution, Khamenei served as Iran’s third president from 1981 to 1989, guiding the country through eight years of war with Iraq. He succeeded Khomeini as Supreme Leader in 1989 after Khomeini’s death.
Khamenei, as the Supreme Leader, is the single most influential player in Iran’s labyrinthine political structure. He has the final say over all domestic and foreign policy decisions. His preferred style of management is staying above the political fray and directly intervening only when actors step out of boundaries he has established or when he feels the stability of the regime to be at risk. 
Khamenei strives to establish Iran as a regional hegemon by driving the U.S. out of the Middle East and extending the influence and authority of the Islamic Revolution. Khamenei, not the president, is the commander-in-chief of Iran’s armed forces. The Quds Force, the paramilitary wing of the Islamic Revolutionary Guards Corps (IRGC) responsible for external operations in places like Iraq and Syria, bypasses IRGC leadership and reports directly to Khamenei.
The contested 2009 presidential elections posed one of the greatest challenges to Khamenei’s authority. Protesters alleged electoral fraud in Mahmoud Ahmadinejad’s victory over reformist candidate Mir Hossein Mousavi. The protests called for greater civil rights within the Iranian political system in addition to disputing the election results. Mass protests, the largest reaching three million, continued even after Khamenei officially endorsed the election results and demanded an end to demonstrations. Under Khamenei’s watch, leaders of the protest movement were arrested in show trials, media outlets with ties to the movement were censored or shut down, and security forces suppressed demonstrations by beating, arresting, and sometimes killing protesters. Reformists remain marginalized from the political system.
Iran would not have agreed to the nuclear deal with the international community in 2015 without Khamenei’s blessing. Khamenei nonetheless claims that the U.S. seeks to exploit the nuclear deal as a front to facilitate regime change. He has therefore instructed Iranians to stay vigilant to prevent malign foreign influence. Khamenei insists that the deal will not improve relations with the U.S. and has repeatedly forbidden non-nuclear negotiations, thereby preventing a broader rapprochement between the U.S. and Iran despite the accord.
-- Christopher Beckmann
 Vali Nasr, “Meet ‘The Decider’ of Tehran. It’s Not the Hothead You Expect,” Washington Post, December 9, 2007. Available: http://www.washingtonpost.com/wp-dyn/content/article/2007/12/07/AR2007120701614_pf.html
 Karim Sadjadpour, “Reading Khamenei: The World View of Iran’s Most Powerful Leader,” Carnegie Endowment for International Peace, 2009, 21-22. Available: http://carnegieendowment.org/files/sadjadpour_iran_final2.pdf
 Julian Borger and Robert Tait, “Iran Elections: mass arrests and campus raids as regime hits back,” The Guardian, 2009. Available: https://www.theguardian.com/world/2009/jun/17/iran-election-protests-arrests1
 “Iran News Round Up,” AEI’s Critical Threats Project, September 16, 2015, http://www.irantracker.org/iran-news-round-september-16-2015.
 Carol Morello, “Ayatollah says nuclear deal will not change Iran’s relations with U.S.,” The Washington Post, July 18, 2015, https://www.washingtonpost.com/world/national-security/ayatollah-says-nuclear-deal-will-not-change-irans-relations-with-us/2015/07/18/7470b531-ff12-4913-81e1-21101130fbdd_story.html.