I would say that a bit more detail would be useful here.  If you are speaking of the Islamic Revolution that happened in Iran in the late 1970s and early 1980s, I would say that the key event would be the facilitation of the overthrow of the Shah of Iran by the Ayatollah.  Being able to successfully facilitate the revolution from abroad through the use of underground tapes that helped to foment the call for a more fundamentalist interpretation of religion in Iran would count in my mind as a critical and key event in the transferal of power.  Another key event would be the radical transformation of Iranian society under the Ayatolllah.  From a very pro- Western social setting, the demand of adherence to a more fundamentalist approach transformed the lives of men and women throughout Iran from what they were and how they carried themselves to what they were supposed to be under the new regime.