Backgrounder: Iran's presidential elections in a glance

The 1979 revolution in Iran, led by Ayatollah Ruhollah Mousavi Khomeini, transformed the U.S.-backed and monarch-ruled country into a republic system under the Islamic ideology.

Established as the Islamic republic, the new ruling system held first presidential election on Jan. 25, 1980, in which Abolhassan Banisadr, a politician and economist, was elected as the first president in Iran's history.

As the president reaping 75.6 percent of the votes, he was the advocate of market economy and was at odds with conservative-dominated parliament and rivals, which ultimately resulted in his dismissal from office after being impeached by the parliament for incompetence on June 21, 1981.

Following this disturbing political experience in the early life of the Islamic republic, Mohammad-Ali Rajaei, the prime minister, was elected the president of Iran on Aug. 2.

Rajaei was assassinated on Aug. 30, 28 days after assuming his presidency.

For the second time in 1981, the Iranians went to the ballot boxes, and Ayatollah Ali Khamenei, the incumbent Supreme Leader, was picked as the third president winning over 95 percent of the votes.

Khamenei became the first cleric to serve in the office from 1981 to 1989. His term in the office fell in during the Iran-Iraq War that left millions killed and injured.

He helped guide the country during the war in the 1980s. As the president, he had a reputation of being deeply interested in the revolutionary ideas, anti-U.S. sentiments, military development, resilient economy, and administrative details.

Akbar Hashemi Rafsanjani, another Iranian cleric and moderate politician, was elected president of Iran by an overwhelming margin shortly thereafter and was in the office from 1989 to 1997.

Rafsanjani showed political skills in promoting his pragmatic policies, favoured Iran's international engagement and renewed its ties with Europe as part of a strategy to use foreign investment and free enterprise to revive the country's war-torn economy.

In the 1997 elections, the reformist Mohammad Khatami was one of the four candidates to run for presidency and was open on social and political reforms. With strong support from the country's youth, women, and intellectuals, he was elected the fifth president by almost 70 percent of the vote.

Khatami advocated increased contact with the United States, but his domestic opponents hindered rapprochement between the two countries. Khatami was reelected in 2001 by an overwhelming majority of the vote for another four years until 2005.

In 2005, Mahmoud Ahmadinejad defeated his moderate rival, Hashemi Rafsanjani, and became president.

Ahmadinejad presented himself as a populist, focusing on issues such as poverty and social justice. He was very active in foreign affairs, vigorously defending Iran's nuclear program against the West criticism and propagating anti-Zionist opinion.

On June 12, 2009, the presidential results indicated that Ahmadinejad had secured an outright victory, achieving more than 60 percent of the vote.

His second term, which ended in August 2013, was featured with a confrontation with the Khamenei and the parliament.

In March 2013, the moderate Hassan Rouhani entered the race for president, positioning himself as a critic of the outgoing Ahmadinejad's economic policies and confrontational approach to foreign affairs.

Rouhani won a commanding victory, taking more than 50 percent of the vote in the June 14 election.

Following Rouhani's inauguration in August 2013, he launched a diplomatic campaign to improve Iranian engagement with the West.

Rouhani's pledge to restart international dialogue regarding Iran's nuclear activities was fulfilled in early November 2013 with the opening of talks between Iran and a group comprising the United States, China, Russia, France, Germany, and the United Kingdom.

The agreement was reached in July 2015 that required Iran to reduce its nuclear stockpile and allowed inspections of its nuclear facilities in exchange for gradual reduction of sanctions.

On April 21, out of 1,636 registered candidates, six were qualified, including three principalists, or conservatives as they are commonly referred to, two centrists and one reformist, to compete for a four-year term as the president.

On Monday, however, Tehran's mayor Mohammad Baqer Qalibaf, a conservative candidate said in a statement that he decides to withdraw from the presidential race to back another candidate Ebrahim Raisi, who is also a conservative nominee.

For May 19 vote, the centrists, led by the President Rouhani, are hoping not to lose their current sovereignty.

If no candidate garners more than 50 percent of the votes, a runoff will be held on May 26 between the two top vote-getters. Endit