Ruhollah Mousavi is the family name of Ayatollah Khomeini. The latter part of his name came from the city he was born in (Khomeyn) and the first part of his name came from studying the Islamic theology where he attained the rank of Ayatollah. "Ayatollah" is a religious title that carries no political significance.
In 1962, the Shah of Iran signed a bill that allowed the use of any holy scripture while an oath is being taken. This offended Khomeini, who asserted that the Koran is the only appropriate book to be used when taking an oath.
Due to his vocal opinions, the Ayatollah was exiled to Turkey, then Iraq in 1964. During his exile, Khomeini arrived at the idea of a theocracy.* That old idea would drastically alter a large, apolitical branch of Islam.
Employing accusations against the shah, and then the shah's son, Khomeini found a way to succeed the royal regime and in 1978, Iranian student demonstrations overwhelmed the shah’s regime. The shah fled to the United States in 1979 and Khomeini established an Islamic dictatorship.
The same year, student radicals overran the United States embassy, taking everyone hostage, and told the United States they would not let anyone go until the shah was released or dead. The 52 hostages still there were finally released 444 days later on Ronald Reagan's inauguration day: January 20, 1981, following the the shah's death of cancer.
Khomeini remained the supreme leader of Iran until his own death on June 3, 1989.