Saeed Jalili, Iran's hardline nuclear negotiator who on Saturday entered the presidential race unexpectedly, became an instant favourite because of his close allegiance to all-powerful supreme leader Ayatollah Ali Khamenei.
Jalili is known for his tough stance in talks between Iran's nuclear team and world powers over Tehran's controversial atomic activities, which the West fears are aimed at developing a military capability -- a claim denied by the Islamic republic.
In negotiations with world powers, he represents Khamenei who has the final say on all key state affairs, including the nuclear programme.
Jalili, soft-spoken but with a rigid, religious persona, has also worked at Khamenei's office.
The 47-year-old hopes to rally the country's traditional voters based on his unwavering loyalty to Khamenei.
His positions on domestic issues, policies and the economy are unknown. Jalili also rarely appears in public.
Born in the holy city of Mashhad in northeast Iran in 1965, Jalili is a veteran of the Iran-Iraq war in the 1980s in which he lost the lower part of his right leg.
After graduating from Tehran's Imam Sadeq University, known for traditionally educating many of Iran's conservatives, Jalili moved up the ranks after joining the foreign ministry in 1989, where he served for 18 years.
Jalili speaks English and Arabic and has a doctorate in political science, according to websites dedicated to him.
In September 2005, shortly after the inauguration of President Mahmoud Ahmadinejad, Jalili was appointed as a deputy foreign minister.
Two years later, in October 2007, he became the secretary of the Supreme National Security Council, one of whose vital tasks is dealing with the nuclear issue.
Since then, he has conducted several rounds of negotiations with the so-called P5+1 group of five permanent members of United Nations Security Council -- Britain, China, France, Russia and the United States -- plus Germany.
Jalili relentlessly stands his ground in reiterating that Iran will not give up "its right to nuclear energy," which Tehran says includes enrichment.
"We believe that the right to enrich is an inalienable right of the Iranian people -- whether we are talking about (to a level of) five percent or 20 percent," said Jalili after the last round of talks in Almaty.
The talks, according to the European Union's top diplomat Catherine Ashton who represents the P5+1, proved that Iran and the world powers stood "far apart" on the nuclear issue.