It's a complex story.

https://tnimage.s3.hicloud.net.tw/photos/shares/AP/20190201/...

Also I am not sure "democratic movement" is at all correct. There was a revolution but the leading groups behind it were decidedly not democratic.

I was a newly minted teen in Tehran when this happened. Ostensibly the trigger event was an anonymous op-ed in a leading Tehran daily that strangely dragged the name of Khomeini back into center stage.

https://www.thenationalnews.com/world/mena/forty-years-since...

At that time, Khomeini was in exile in Iraq under the watchful eyes of Sadam Hussein.

Two basic dynamics set the revolution into motion. Leftist and Islamist. The leftists were card carrying USSR affiliates Tudeh Party (The Masses), various student-cum-revolutionary Marxists, Marxists-Leninists, Maoists, etc. Prominently (because of their armed attacks on police stations, banks, etc. earlier in 70s) there was hard left secular Fadayein and "Islamic-Marxist" Mujahedin Khalgh (MKO, ..., they have a whole collection of acrynoms).

Mujahedin had a sort of spiritual guide in Ayatollah Taleghani. But for a good while after the overthrow of the regime, they went around mouthing "Imam Khomeini" until the said Imam decided he didn't need them anymore. But we digress. Taleghani was one of the reasons people were beguiled because he made very socialist/democratic pronouncements. He ended up dying "suddenly" a few months after revolution, when Khomeini was asserting his demi-god status. So "democratic"? Well, the communists are democratics in their sense of the word, kinda like CPC is democratic if you ask them. As for MKO, a brief review of their sordid history and that whole bizare show they have going on with their all female army and female leader (complete with Hijab) also should give you an idea regarding their "democratic" credentials.

https://en.wikipedia.org/wiki/Mahmoud_Taleghani

Among the Islamists, you had people like Chamran. A genius geek who went Islamist radical. He started what became Hizbollah (or Amal). [He said he worked at Bell Labs and JPL.]

https://en.wikipedia.org/wiki/Mostafa_Chamran

The only group having any real claims to "democratic" leanings were the National Front. Their leadership made a foolish error and went to Paris to kiss the ring. Khomeini may have enjoyed humiliating them. A lone dissenter from National Front, Shapur Bakhtiar accepted to become PM before Shah left Iran. He was the lone sane voice asking pointed questions about the "holy man who lies" and refusing to kiss the ring.

Khomeini in the interim flew into Tehran on Air France (yes! French military pilots, and packed with press, spooks, and handlers) and got a frenzied reception, and immediately upon touch down pretty much told all the also-rans to basically go fuck themselves.

Bakhtiar at this point, still head of the last government of Pahlavi dynasty, was betrayed by some key members of the military leadership. They started direct negotiations with Khomeini, at the urging of an American General (who flew to Iran before Shah left). This is what is alleged by former regime officials and military (see Harvard's Iran Oral History Project) but denied by the said general. Regardless, the military declared itself "neutral".

Bakhtiar did escape to Paris but ended up getting butchered (literally) by IR regime goons sent after him.

https://en.wikipedia.org/wiki/Shapour_Bakhtiar

MKO and Khomeini later go on to lock horns, including spectacular assassinations by MKO and massive execution sprees by the Ayatollah.

https://en.wikipedia.org/wiki/Sadegh_Ghotbzadeh

Sadegh Ghotbzadeh, who used to have a little Islamist revolutionary office right on Dupont Circle -- oh yes -- and who none other than Robert F. Kennedy intervened on his behalf to prevent his deporation -- visa issues -- is an interesting character and no doubt many quarters are happy he is quite dead. Now, Sadegh, unlike the guy from Green Book, didn't play the piano and was quite a ladies man, the very smooth and English speaking voice and face of Ayatollah in Paris and then later in Iran, so I am not exactly sure why RFK felt his personal intervention was necessary.

He was executed by Khomeini later on after admitting under torture to being a CIA agent.

https://www.washingtonpost.com/archive/politics/1979/12/13/g...

"Only the timely intervention of a New Jersey senator and then-Attorney General Robert F. Kennedy saved him from a quick deportation. as a communist to face charges of treason in Iran." [that's actually funny.]