SAVAK is the Roman abbreviation of "Sazman-e Etelaat Va Amniat Keshvar" (Organization of Intelligence and Security of the Country) in Persian (Farsi) letters.
According to Ervand Abrahamian, the Israeli intelligence service (Mossad), the CIA and the FBI assisted the Shah's regime in establishing SAVAK in 1957 (Iran Between Two Revolutions 1982, 419). Officially, the Prime Minister's Office supervised SAVAK whose head was the Deputy Prime Minister (Radical Islam: The Iranian Mojahedin 1989, 13).
Abrahamian suggests that SAVAK gradually expanded its networks all over Iran, enabling it to scrutinize anyone recruited into the university, the civil service and the large industrial plants (Iran Between Two Revolutions 1982, 420). By 1977, SAVAK had 5,300 full-time agents and a large number of part-time informers (Ibid., 436). It had the power to "censor the media, screen applicants for government jobs, ... and use all means necessary, including torture, to hunt down dissidents" (Ibid.).
Abrahamian holds that the Tudeh Party was one of the major targets of SAVAK even in the 1970s when the party was no longer a serious threat to the Iranian regime (Iran Between Two Revolutions 1982, 451).
Abrahamian maintains that in the 1970s, SAVAK and the Police formed a joint committee (Anti-Sabotage Joint Committee) to coordinate their activities against the opponents of the Shah (Radical Islam: The Iranian Mojahedin 1989, 38).
According to Mohsen M. Milani, SAVAK was created through the assistance of the Mossad and the CIA in 1957 (The Making of Iran's Islamic Revolution: From Monarchy to Islamic Republic 1988, 8)
The source claims that SAVAK extended its control over all the professional associations (such as trade unions) and allowed the formation of apolitical student associations only (Ibid., 115). Because of the SAVAK control, newspapers critical of the regime had difficulty obtaining a license to publish (Ibid.).
Milani claims that in the 1960s and 1970s, SAVAK focused on the suppression of leftist organizations which led to the arrest of a large number of prominent activists including the ideological founders of the future the "Fadayean Khalq Organization" (The Making of Iran's Islamic Revolution: From Monarchy to Islamic Republic 1988, 137). The continuation of suppression resulted in the killing of 106 members of the mentioned organization and paralysis of the group by 1977 (Ibid.).
Milani maintains that by 1977, SAVAK already paralysed all the organized anti-regime groups, ranging from the left to the right (The Making of Iran's Islamic Revolution: From Monarchy to Islamic Republic 1988, 129, 185). Most of the opponents to the Shah were imprisoned, killed or in exile in the late 1970s (Ibid., 185).
Milani holds that during the Islamic Revolution, the Shah and then Dr. Bakhtiar (last prime minister of the Shah) began to limit SAVAK through a variety of measures including the demotion of a number of high-ranking officers, replacement of the notorious long-lasting chief, General Nassiri, and restriction of its power (The Making of Iran's Islamic Revolution: From Monarchy to Islamic Republic 1988, 195, 202). Shortly before the collapse of the Shah's regime, Dr. Bakhtiar dissolved SAVAK in January 1979 (Ibid., 227).
According to Amnesty International, the head of SAVAK, who was appointed by the Shah, exercised unlimited power (November 1976, 1). SAVAK was in charge of the suppression of political opposition in Iran and abroad wherever there was an Iranian community (Ibid., 1, 2). Accordingly, many Iranian students in foreign countries were arrested upon their arrival in Iran because of their political activities abroad (Ibid., 2).
Tahmoores Sarraf claims that SAVAK destroyed most of the opposition groups in the 1960s and the 1970s as a result of which there was no strong organized political alternative to Khomeini during the Islamic Revolution (Cry of a Nation: The Saga of the Iranian Revolution 1990, 40). In the wake of the Revolution, those who in one way or another, had ties with SAVAK were arrested, imprisoned, executed and/or had their properties confiscated (Ibid., 51).
Gholam R. Afkhami claims that, in addition to the suppression of political opponents, SAVAK even harassed the Shah's supporters by creating an intentional sentiment of intimidation within different governmental and non-governmental institutions (The Iranian Revolution: Thanatos on a National Scale 1985, 186).
According to Dilip Hiro, the Shah directly controlled SAVAK despite its official attachment to the Prime Minister's Office (Iran Under the Ayatollahs 1987, 54). The source claims that SAVAK exercised its policy of intimidation of political opponents through a number of measures such as "harassment; interference with mail and telephone; denial of job, promotion, passport or exit visa; pressure on the suspect's family and friends; arrest without charge; lengthy detention without trail; exile to outlandish places in the country; and the threat of murder" (Ibid.). Hiro claims that SAVAK had the power to "interrogate, imprison and eliminate opponents without challenge or scrutiny" (Ibid.). It became notorious because of its brutality especially towards guerrilla organizations (Ibid., 63).
Jerrold D. Green claims that, among other tasks, SAVAK (with the assistance of the Gendarmerie) performed the day-to-day security tasks of the country (Revolution in Iran: The Politics of Countermobilization 1982, 126)
For further information, please refer to the attached documentation.
Attachments

Abrahamian, Ervand. Iran Between Two Revolutions. Princeton, New Jersey: Princeton University Press, 1982, pp. 38, 419, , 420, 436 and 451.

Abrahamian, Ervand. Radical Islam: The Iranian Mojahedin. London: I.B. Tauris & Co. Ltd., 1989, p. 13.
Afkhami, Gholam R.. The Iranian Revolution: Thanatos on a National Scale. Washington, D.C.: The Middle East Institute, 1985, p. 186.
Amnesty International. "Amnesty International Briefing: Iran." November 1976, pp. 1, 2.
Green, Jerrold. Revolution in Iran: The Politics of Countermobilization. New York: Praeger, 1982, p. 126.
Hiro, Dilip. Iran Under the Ayatollahs. London: Routledge & Kegan Paul, 1987, pp.54, 36.
Milani, Mohsen M.. The Making of Iran's Islamic Revolution: From Monarchy to Islamic Republic. Boulder: Westview Press, 1988,
pp. 8, 115, 129, 137, 185, 195, 202 and 227.
Sarraf, Tahmoores. Cry of a Nation: The Saga of the Iranian Revolution. New York: Peter Lang, 1990, pp. 40, 51.