Equatorial Guinea's President Teodoro Obiang Nguema is the world's longest serving leader with his 44-year rule. He is followed by Cameroon President Paul Biya (41 years), Republic of Congo President Denis Sassou Nguesso (39 years), Uganda President Yoweri Museveni (37 years) and Tajikistan President Emomali Rahmon (31 years). Eritrea President Isaias Afwerki is also on the list.