Terrorism has been a recurrent challenge for Iran since the 1979 revolution. The perpetrators, targets and frequency have fluctuated. The early attacks killed hundreds of government officials, including a president, prime minister, cabinet ministers, and dozens of members of parliament. Attacks have been carried out by a wide array of actors—ethnic separatists, Sunni militants, monarchists, Marxists and, statistically most of all, the opposition Mujahadeen-e Khalq (MEK). In 2017, the Islamic State of Iraq and Syria—a Sunni military group—launched its first attacks against the Islamic Republic, a predominantly Shiite country.