Botswana's former President Festus Mogae has won a $5m (£2.8m) prize to encourage good governance in Africa.
He stepped down in April after serving two terms in office.
Botswana is one of Africa's most stable countries - it has never had a coup and has had regular multi-party elections since independence in 1966.
Announcing the prize, ex-UN Secretary General Kofi Annnan also commended Mr Mogae for his action to tackle the Aids pandemic which has ravaged the country.
The Ibrahim Prize - the most valuable individual annual prize in the world - was set up by Sudan-born telecoms entrepreneur Mo Ibrahim.
As well as the $5m prize, Mr Mogae gets $200,000 a year for the rest of his life.
"President Mogae's outstanding leadership has ensured Botswana's continued stability and prosperity in the face of an HIV/Aids pandemic which threatened the future of his country and people," Mr Annan said.
Botswana is the world's biggest diamond producer but unlike other resource-rich countries in Africa, this has not become a source of conflict.
"Botswana demonstrates how a country with natural resources can promote sustainable development with good governance, in a continent where too often mineral wealth has become a curse," Mr Annan said.
Mr Annan also noted that Mr Mogae had tried to diversify Botswana's economy away from its reliance on diamonds.
In 2006, President Mogae's government introduced a law curbing the sale of alcohol and banning it on Sunday.
He blamed alcohol for the spread of HIV/Aids, among other problems.
But Mr Mogae also came in for criticism from lobby group Survival International for Botswana's policy of relocating Bushmen groups away from their traditional homes in the Kalahari desert.
Mr Mogae was succeeded as president by Seretse Khama Ian Khama in April.
Former Mozambican President Joaquim Chissano won the inaugural Ibrahim Prize last year.