Congo-Léopoldville, known as Congo-Kinshasa after 1966, was a Central African country that existed from 1960 to 1971. With its capital at Leopoldville (Kinshasa), the republic's first president was Joseph Kasa-Vubu, while its first prime minister was Patrice Lumumba. The government was unstable and fought against the rival Congo-Stanleyville, South Kasai, and Katanga governments during the Congo Crisis, and Lumumba was imprisoned and executed in 1961 after Joseph-Desire Mobutu led a military coup against the pro-Soviet Lumumba. After United Nations Secretary-General Dag Hammarskjold's 1961 death in a plane crash, UN peacekeepers actively supported the Leopoldville government against the secessionist movements, and the government unified the Congo after crushing the secessionist states and the Maoist Simba Rebellion. In 1965, Mobutu seized power as dictator, and he renamed the Congo to "Zaire" (now the Democratic Republic of the Congo) in 1971.