who is the longest serving president in west africa?
['Paul Biya. Cameroon. Prime Minister, then President. ... ', 'Teodoro Obiang Nguema Mbasogo. Equatorial Guinea. President. ... ', 'Ali Khamenei. Iran. President, then. ... ', 'Denis Sassou Nguesso. Republic of the Congo. President. ... ', 'Hun Sen. Cambodia. Prime Minister. ... ', 'Yoweri Museveni. Uganda. President. ... ', 'Idriss Déby. Chad. President. ... ', 'Nursultan Nazarbayev. Kazakhstan.']