PENPIX-Main figures in Iran's presidential election

May 9 (Reuters) - Iranians vote on June 12 in a presidential election that will show their views on the performance of hardline incumbent Mahmoud Ahmadinejad.

Ahmadinejad and his main moderate rivals have officially declared their candidacies in the election, signing up during a five-day registration period that ends on Saturday.

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.

Following are brief portraits of the Islamic Republic's supreme leader and the main contenders in the poll.

AYATOLLAH ALI KHAMENEI

As supreme leader, Khamenei wields ultimate authority under Iran's system of clerical rule known as "velayat-e faqih", or guardianship by an Islamic legal scholar. Not himself elected by popular vote, his wishes can strongly influence elections, which are conducted within rules set by the clerical leadership.

Khamenei, a critic of the United States, is a conservative who plays a balancing role among Iran's competing power centres. He has rarely championed reformist causes. The 69-year-old cleric took office in 1989 after the death of Ayatollah Ruhollah Khomeini, who led Iran's 1979 Islamic revolution that toppled the U.S.-backed monarchy.

MAHMOUD AHMADINEJAD