TIMELINE: Iran's road to presidential elections

(Reuters) - Hardline President Mahmoud Ahmadinejad resoundingly won Iran's election, preliminary official results showed on Saturday, but his moderate challenger alleged irregularities and claimed victory for himself.

Iran, the world's fifth biggest oil exporter, is grappling with the impact of the global economic downturn and weighing its response to U.S. President Barack Obama's diplomatic overtures.

Here is a timeline of the main political events since the 1979 revolution and founding of the Islamic Republic:

January 1979 - Shah Mohammad Reza Pahlavi is forced into exile after mounting discontent with his authoritarian rule.

February 1979 - Ayatollah Ruhollah Khomeini returns to Tehran from Paris after 15 years of exile spent mainly in Iraq and quickly consolidates his power to become Supreme Leader.

June 1989 - Khomeini dies. Ayatollah Ali Khamenei, a former president, is appointed Supreme Leader.

August 1989 - Pragmatic deal-maker Akbar Hashemi Rafsanjani becomes president after landslide election win.

May 1997 - Reformist Mohammad Khatami is elected president in surprise and sweeping victory over candidate backed by conservative clerics.

July 1999 - Student unrest turns violent over closure of pro-reform newspaper. Dozens of such newspapers are later shut.