Politician and professor Mustafa Moin is currently an adviser to Iran's outgoing President Mohammed Khatami and has attracted some significant backing.
His presidential bid has been supported by several reformist parties and organisations, but most importantly by the Islamic Iran Participation Front (IIPF).
The 54-year-old was the first candidate to publicly announce his election bid last December. However, he was promptly disqualified by the Guardian Council - an unelected body that exists, it says, to protect the republic.
His candidate status was restored on 24 May due to political pressure from Supreme Leader Ayatollah Ali Khamenei.
Moin's campaign has since been managed by Ali Shakouri-Rad - a politician who was also banned by the Guardian Council from running for Majlis or parliament in 2004.
Political experience
A paediatrician by training, Moin's political career began in 1982 - when he was elected to represent the province of Shiraz in the Islamic republic's first Majlis following a mid-term ballot.
Rising through the ranks, he became the minister of culture and higher education during Akbar Rafsanjani's presidency (1989-1993) and again during Khatami's first term in office.
By 2000, Moin was heading the Ministry of Science, Research and Technology but chose to resign on two separate occasions - the first after mass student demonstrations in July 1999 and again in July 2003 after failing to get legislation past the Guardian Council.