Aelf,
A mean, the president in Iran is not like in the USA, he has no control over the armed forces. The revolutionary guard, in particular, is like a paralel army with an economic clout over the iranian economy.
So they have a president, who governs over a consil of ministers, but there is a supreme leader which controls all armed forces, all religious institutions (it is a teocracy after all) and some other institutions (national radios, the highest positions in the judiciary, etc).
Besides the armed forces there are the Guardians of the Revolution, a paralell army, or the real army. They manage the key military projects (like the missiles), and have their own navy and air forces. As the name indicates they are the real regime supporters and in many ways the real power that have to be defeated for a change to be possible. It was reported that amidst large revolts in the last election, Ahmadinejad was slapped by the Revolutionary Guard Chief of Staff for suggesting more freedom of the press.