First a trip to N'Djamena at the end of the year, then another just weeks later. Ali Modu Sheriff, the former governor of Nigeria's Borno State from 2003 to 2011 and now a multimillionaire, known in the region as "SAS", has built up strong ties with the Chadian ruling family over two decades. He even owns a large house in the centre of N'Djamena. Born in the Chadian part of Kanem-Bornou, an empire founded in the 8th century that straddles present-day Chad and Nigeria, the 66-year-old has formed precious