Final answer:
Ayatollah Ruhollah Khomeini replaced Shah as the leader of Iran in the late 1970s and had negative views of the United States, culminating in the hostage crisis where 52 Americans were held for 444 days.
Step-by-step explanation:
The leader who replaced Shah as the leader of Iran in the late 1970s was Ayatollah Ruhollah Khomeini. After a series of events, including strikes and protests against the Shah's regime, Khomeini, who previously had been exiled, returned triumphantly to Iran. The overthrown Shah then fled the country in January 1979. Khomeini's views on the United States were markedly negative, particularly because the U.S. had supported the Shah's regime and his policies that favored Western oil interests. The disdain for the United States was evident when, on November 4, 1979, Iranian students stormed the U.S. embassy in Tehran, taking 52 Americans hostage in response to the U.S. allowing the Shah to enter the country for medical treatment.
The hostage crisis lasted for 444 days and reflected the deeply rooted anti-American sentiment based on historical interventions by the U.S. in Iran's political affairs. Khomeini's leadership ushered in an Islamic Republic, with a constitution emphasizing that all laws must conform to Islamic law, and significantly shifted Iran's approach to the West, especially the United States, which was seen as an adversary.