Yes, "He is one of Africa's longest serving leaders having been in office for decades" is correct!!
Next Quesiton:

Who is this hookah-smoking fellow?
  1. Turkish President Recep Erdogan
  2. Syrian President Bashar al-Assad
  3. Mexican President Enrique Peña
  4. Egyptian President Hosni Mubarak
  5. Libyan leader Muammar Gaddafi