There was none. Ever since the founding of the Persian Empire, which happened many centuries B.C. Iran was always under a Shah (king.)
The last change between dynasties occurred in 1925 when Reza Khan Pahlavi led a military coup that successfully overthrew Ahmed Qajjar of the Qajjar Dynasty (which had been in power since the 1700s). It is Reza Pahlavi and his son Mohammed Reza Pahlavi who are usually referred to in the West as the "Shah", but as mentioned above, this term is very old. Mohammed Reza Pahlavi was overthrown in the Islamic Revolution.
There was no leader before him Iran was a monarchy before the Islamic Republic and the king (natively called "Shah") was Mohammadreza Pahlavi.
Reza Shah
The ayatollah took over after shah of iran lost power.
Ayatollah
the shah of iran was replaced by ayatollah ruholla kahmeini
Shah Mohammed Reza Pahlavi
reza khan or reza shah or king reza
Mohammed Reza Pahlavi
by Shah you probably mean the King of Iran before Islam revolution in Iran. people considered him as a dictator and made an revolution based on Islam and made Islamic republic of Iran and Shah escaped from Iran and said I am sick and I go for a medicine trip. but never backed to Iran.
ayatollahkhomeini
he was a King in ancient Persia (Iran) and it was much before Islam enter Iran.
Shah