Iranians head to the polls Friday to vote in the Islamic Republic's presidential election. The contest is largely seen as a referendum on the incumbent president's more moderate political stance, which helped pave the way for the country's nuclear deal with world powers.

President Hassan Rouhani is widely seen as the front-runner after his moderate administration struck the atomic accord. He could face tough competition from hard-line cleric Ebrahim Raisi, who is perceived to be close to Supreme Leader Ayatollah Ali Khamenei. Two other candidates also are running.

Under Iran's constitution, the supreme leader has final say on all state matters. Iran's president is subordinate but still powerful, with considerable influence over both domestic policy and foreign affairs.

Here's a look at the candidates competing.

HASSAN ROUHANI

Rouhani, 68, is a moderate cleric elected in 2013 on pledges of greater personal freedoms and improved relations with the West. His government negotiated the 2015 nuclear deal, which saw Iran accept curbs on its nuclear program in exchange for relief from crippling international sanctions.

Rouhani has faced pushback from conservatives and hard-liners, who criticize the accord as giving too much away. Since the deal went into effect, Iran has doubled its oil exports and inked multi-billion-dollar aircraft deals with Boeing and Airbus. But critics of the deal say the economic benefits have yet to reach ordinary Iranians. The poor, both young and old, can be seen in Iranian cities searching trash for food or cleaning car windows for loose change.

Early in his tenure, Rouhani shared a 2013 phone call with then-U.S. President Barack Obama, the highest-level exchange between the two countries since Iran's 1979 Islamic Revolution and the U.S. Embassy hostage crisis. During the campaign, Rouhani also increasingly has criticized Iran's powerful Revolutionary Guard, a hard-line paramilitary force answering only to Khamenei, something he so far has been hesitant to do while in office.

EBRAHIM RAISI

Raisi, 56, is a hard-line cleric close to Khamenei who has vowed to combat poverty and corruption. He could pose the biggest challenge to Rouhani, especially if he can unify hard-liners. Raisi also has promised monthly cash payments to the poor, a populist move that's been popular with Iranian voters in the past.

Last year, Khamenei appointed Raisi as head of the Imam Reza charity foundation, which manages a vast conglomerate of businesses and endowments in Iran. Khamenei called Raisi a "trustworthy and highly experienced" person, causing many to wonder if he might also be a possible successor to the supreme leader himself.

Raisi, who works as a law professor, previously served as an attorney general and Iran's deputy judiciary chief. Two major clerical bodies, which declined to endorse anyone in the 2013 election, have backed Raisi in a snub to Rouhani, who himself is a cleric himself.

However, his candidacy also has revived the controversy surrounding the 1988 mass execution of thousands in Iran, one of the darkest moments of Iran's post-revolution history still not recognized by its government. Raisi allegedly served on a panel involved in sentencing the prisoners to death. While he hasn't commented publicly on the accusation, his supporters appear to have released a video offering a hard-line justification for the executions.

MOSTAFA HASHEMITABA

Hashemitaba, 70, served as minister of industry in the 1980s. He is a pro-reform figure who previously ran for president in 2001.

MOSTAFA MIRSALIM

Mirsalim, 69, was shot and wounded during the unrest leading up to the 1979 revolution. He went on to serve as deputy interior minister and police chief. He served as culture minister for four years under Rafsanjani.