About 18 ethnic groups inhabit Sierra Leone; the two largest and most influential ones are the Temne and Mende peoples. About 2% of the country's population are Creole people, descendants of freed African American and West Indian slaves. English is the official language used in schools and government administration; however, Krio is the most widely spoken language across Sierra Leone, spoken by 97% of the country's population. Sierra Leone is rich in natural resources, especially diamond, gold, bauxite and aluminium. The country is a member of the United Nations, African Union, Economic Community of West African States (ECOWAS), Mano River Union, Commonwealth of Nations, IMF, World Bank, WTO, African Development Bank, and Organisation of Islamic Cooperation. Sierra Leone is home to Sub-Saharan Africa's first Western-style university: Fourah Bay College (established in 1827).