Fab four: More than 450 Iranians registered to run for president, but the 12-member Guardian Council only gave its seal of approval to four, pictured above. Clockwise from top left, they are: Mahmoud Ahmadinejad, the current president; Mir Hossein Mousavi, a reformist who was prime minister from 1981 to 1989; Mohsen Rezai, a conservative and former commander of the Revolutionary Guard; and Mehdi Karroubi, a moderate and former speaker of parliament. According to Iran's Constitution, candidates must be politicians or clerics, hold Iranian citizenship, and be Shiite Muslims who believe in the principles of the Islamic Republic. (Harvard University's Kayhan Barzegar has more on the policies and promises of all four candidates in this week's List.)