Supreme Leader: Ayatollah Ali Khamenei
The Supreme Leader - the highest power in the land - appoints the head of the judiciary, military leaders, the head of radio and TV and Friday prayer leaders. He also confirms the election of Iran's president.
Moreover, the Supreme Leader selects six members of the 12-member Guardian Council, an influential body which has to pass all legislation and which can veto would-be election candidates.
The Leader is chosen by the clerics who make up the Assembly of Experts. Ayatollah Ali Khamenei was appointed for life in June 1989, succeeding Ayatollah Khomeini, the founder of the Islamic republic. He previously served two consecutive terms as president in the 1980s.
He has intervened on behalf of conservatives, coming into conflict with former president Mohammad Khatami and other reformists.
Ayatollah Khamenei endorsed the results of the disputed presidential election of June 2009, which gave a landslide victory and a second term to his ally, President Mahmoud Ahmadinejad.
However, the unprecedented defiance by opposition supporters to his call for an end to street protests against the result is thought to have undermined his authority.
There were further challenges to his authority during the violent protests that followed the death of leading dissident cleric Grand Ayatollah Hoseyn Ali Montazeri - a prominent critic of Ayatollah Khamenei - in December 2009.
President-elect: Hassan Rouhani
Hassan Rouhani was elected as Iran's president in June 2013, winning just over 50% of the vote.
The cleric, regarded as a religious moderate, was backed by the reformists, led by former President Mohammad Khatami. He was endorsed by former President Akbar Hashemi Rafsanjani, who was barred from running for office.
Mr Rouhani says he wants to steer Iran towards "moderation". One of his main election pledges was to try to ease international sanctions imposed on Iran over its nuclear programme. He has promised greater engagement with the West.
He succeeds ultra-conservative Mahmoud Ahmadinejad, who was re-elected as president in June 2009 amid a bitterly contested poll which led to serious internal unrest.
Mr Ahmadinejad served as Tehran's mayor before winning a run-off vote in elections in June 2005, defeating former president Akbar Hashemi Rafsanjani to become Iran's first non-clerical president for 24 years.
Much of his support came from poorer and more religious sections of Iran's rapidly growing population, particularly in the provinces.
His harsh rhetoric often caused outrage abroad, most notably over Israel and Jews. He likened Israel to a "cancer" and demanded its replacement with a Palestinian state, while describing the Holocaust as a "myth".
Mr Ahmadinejad faced criticism at home over his handling of the economy, with hardship on the rise as a result of falling oil prices and the impact of sanctions.
In 2011 he and Supreme Leader Ayatollah Khamenei became engaged in an unusually public stand-off over the resignation of the intelligence minister. Ayatollah Khamenei steadily isolated Mr Ahmadinejad and persecuted his allies during the remainder of his term as president.