It depends on what you are calling "Iranians".
If you are referring to the Sassanid Empire of the 500s and 600s CE, the Muslims invaded Persia as part of their massive expansion and conquest of neighboring states.
If you are referring to the Iranian Revolution of 1979, there are two suppositions in this question that are incorrect, namely that Muslims and Iranians are different in the Iranian context and that the primary or most important people to overthrow the Shah were fundamentalist Muslims. This is not the case. The Iranian people, most of them traditional or secular Muslims revolted all across Iran. The Religious Fundamentalists were a minority of those Iranians who were protesting. When the Shah abdicated, there was an intent to create a Republic that represented the Iranian People. However, between April and October of 1979 (after the Shah had already departed the country and the Islamic Republic of Iran declared) the Ayatollahs were able to consolidate power and create the Constitution of the Islamic Republic of Iran which vested the Religious Fundamentalists with political power.
Iranians in general were opposed to the Shah and opposed him from nearly every political perspective. These include:
As concerns the specific reasons for the Iranian protests and the eventual revolution, they were numerous:
Wealth & Employment Issues: Most importantly was the wealth inequality between the Shah and the nobility and common Iranian citizen. There was immense poverty throughout the country and high unemployment, underemployment, low wages, and few protections for laborers.
Religious Conservatism: Most Iranians were religiously conservative (similar to the American Bible-belt as opposed to the Fundamentalists) and resisted the Shah's Westernization and Secularization movements in Iran. The Shah made clear that religion was not important to him as a ruler, whereas it was a concern among the people.
Puppet to Foreigners: The Shah was also seen as a Western puppet, especially when the CIA overthrew the Iranian President Mossadegh in 1953 to re-install the Shah of Iran and considering how Iran profited very little from its own petroleum.
Brutal Secret Police: The Shah had a notorious secret police called the SAVAK which harassed people and killed scores of others.
Authoritarianism: Iranians wanted to be in control of their own affairs. Iranians wanted some form of self-government or democracy. The Shah was an authoritarian who prevented people from expressing their own opinions.
Issue for Fundamentalists: Particularly in the fundamentalist camp, the fundamentalists in Iran felt that the Shah epitomized a Western culture of greed and materialism, because he tried to establish a more secular government. As with many rulers, he accumulated vast personal wealth. He also employed various means to suppress political dissent. It was ultimately the exiled Ayatollah Khomeini who in 1979 succeeded the Shah and established an Islamic religious government.
Note: The fact that these grievances existed does not mean that the Islamic Republic of Iran afterwards "fixed" these problems.
I believe that the majority of Iranians are Shi'a Muslims.
"Gods"? As far as I know, most Iranians are muslims, and therefore monotheistic.
The majority of Iranians are Shiites, but there is a large minority of Sunnis, especially among the Balochi minority (which is predominantly Sunni).
Because most Iranians (some 85%) are Shiat Muslims and Imam Hosein (The 3rd Shiat Imam (Cleric)) was killed in Ashura.
2 Muslims should not fight each other
Most Iranians are Shiite Muslims, but there is a minority of Sunni Muslims, Jews, Christians, Baha'i, Yarsan, Yazidi, and Zoroastrians. There are also minor religions that are not often counted as well.Of course, an increasing number of Iranians are Agnostics and Atheists (but remain in-the-closet to avoid apostasy punishments).
"Iranian" is a nationality (those from the country of Iran). The majority of Iranians are Shi'ite Muslims.
The majority of Persians (Iranians) are Shi'ite Muslims and their holy book is the Qur'an a/k/a the Koran.
The majority of Persians (Iranians) are Muslims; more specifically, Shia Muslims. Minorities include Sunna Muslims, Bahá'ís, Christians, and Jews. Especially the Bahá'ís are severely persecuted.
No, he sent Christians to fight. The Turks were Muslims.
The majority of Persians (ie., Iranians) are Shi'ite Muslims, followers of Islam.
Christians and Muslims