Ndong Sima, a 68-year-old economist, served as prime minister under Bongo from 2012 to 2014 before becoming a critic and eventually challenging the longtime leader in elections in 2016 and 2023.
His appointment, announced on state TV on Thursday, was made in a decree by Gabon’s new military leader, General Brice Oligui Nguema, who was sworn in as interim president on Monday.
In his inauguration speech, Oligui vowed to hold “free, transparent and credible elections” to restore civilian rule, although he did not give a timeframe.
He also said he would shortly announce an inclusive transitional government drawing on figures from across the political spectrum.
Disputed elections
Bongo took office in 2009 on the death of his father Omar, who ruled the country for more than 40 years, accruing a personal fortune and a reputation as a kleptocrat.
Ali Bongo was re-elected by a wafer-thin margin in 2016, according to bitterly disputed official results, but two years later suffered a stroke that weakened his grip on power.
On 30 August, soldiers led by Oligui, head of the elite Republican Guard, detained Bongo along with his wife and son, shortly after election overseers declared him the winner of a presidential ballot held four days earlier.
The developments in Gabon are being anxiously followed in central Africa and beyond.
The country, which has large reserves of oil, joins Mali, Guinea, Sudan, Burkina Faso and Niger among the countries in Africa that have undergone coups in the last three years.