(CNN) — The president of the West African nation of Ghana, John Evans Atta Mills, has died, his chief of staff said in a statement Tuesday.

He died at a military hospital Tuesday afternoon a few hours after becoming ill, according to the statement, signed by John Henry Martey Newman. The vice president will address the nation soon, the statement said.

He was 68.

Opinion: Mills’ election victory was a ‘victory for democracy in Africa’

Mills was a former law professor and a tax expert. He was Ghana’s vice president from 1997 to 2000.

Before his political career, he taught at the University of Ghana and also was a visiting lecturer at Temple University in Pennsylvania and Leiden University in Holland.

Mills ran for president unsuccessfully in 2000 and 2004 beforenarrowly winning a runoff in 2009.

U.S. President Barack Obama met with Mills when he visited Ghana in July 2009. Obama praised the country as a model for democracy and stability when Mills visited Washington this year.

“Ghana has become a wonderful success story economically on the continent,” Obama said. “In part because of the initiatives of President Mills, you’ve seen high growth rates over the last several years. Food productivity and food security is up. There’s been strong foreign investment.”

Part of a former British colony, Ghana was among the first African countries to gain independence, in 1957. It endured a series of coups before a military dictator, Jerry Rawlings, took power in 1981. Rawlings led Ghana through a transition to democracy about 10 years later.

Vice President John Dramani Mahama, 53, is a former member of Ghana’s Parliament who has served as director of communication for the National Democratic Congress party.

Obama hailed Ghana as ‘model for democracy’