Mr Guei faced humiliation in 1997 when the president ordered him to be removed from the military after allegations he had tried to plan a coup two years earlier.
General Robert Guei is a long-time nemesis of former President Henri Konan Bedie, who - in a Radio France Internationale broadcast on Friday - called the new leader "the nitwit who has proclaimed himself president".
The 58-year-old general became Ivory Coast's military chief in 1990, but he was fired in 1995 after criticising President Henri Konan Bedie for using the military to suppress student riots.
He went on to be appointed minister of sports, but President Bedie dismissed him from the cabinet for unknown reasons shortly after the Atlanta Olympics in 1996.
He has enjoyed widespread respect in the army and his colleagues in the military give him the nickname "Le Boss".
Mr Guei faced humiliation in 1997 when the president ordered him to be removed from the military after allegations he had tried to plan a coup two years earlier.
He has kept a low profile since then, despite being an ally of opposition leader Alassane Ouattara, who is in exile after courts ordered his arrest on charges of forging citizenship documents to enter presidential elections in 2000.
Promises
BBC correspondent Mark Doyle says General Guei's control over local TV and radio stations is crucial to his claim to power.
He has used his TV appearances to proclaim the usual list of promises by a leader of a coup d'etat - a return to democracy and respect for international agreements.
But he himself has been accused of allowing soldiers to torture student protesters in 1990, and his presidential promises were made with him surrounded by gun-toting soldiers in battledress.
The Ivory Coast has traditionally been one of the most stable countries in Africa, and this coup has come as a surprise and a shock to most people.