The prize has only been awarded five previous times: to Nelson Mandela of South Africa (an honorary laureate) and Joaquim A. Chissano of Mozambique in 2007; to Festus G. Mogae of Botswana in 2008; to Pedro de Verona Rodrigues Pires of Cape Verde in 2011; and to Hifikepunye Pohamba of Namibia in 2014. It was supposed to be an annual prize, but in some years, the selection committee apparently has not found suitable candidates for the award.
Critics say the award sets a low bar for African democracy, rewarding leaders merely for leaving office. But Mr. Ibrahim has insisted that the award recognizes “excellence in leadership.”
The continent is home to several so-called leaders for life, including Joseph Kabila of the Democratic Republic of Congo, who has delayed elections for more than a year and overseen a crackdown on dissent; Yoweri Museveni of Uganda, who favors the scrapping of age limits for holding office; and Paul Biya of Cameroon, who has been in power for 35 years and turns 85 on Tuesday.
But hopes for democracy have revived elsewhere. Last year, Yahya Jammeh of Gambia stepped down under threat of regional military intervention after he lost an election, and Robert Mugabe of Zimbabwe, who had been in power since 1980, was removed as president after an internal party coup.
From 1990 to 2003, Liberia suffered from two civil wars that claimed an estimated 250,000 lives, displaced millions and shattered infrastructure.
Ms. Johnson Sirleaf restructured the military, which, like rebel groups, had committed atrocities during the civil war, and had even once imprisoned her. She also reformed the police and established a Truth and Reconciliation Commission. Ms. Johnson Sirleaf shared the Nobel Peace Prize in 2011, shortly before she won a second term.
However, her government was criticized for its initially slow response to the Ebola epidemic and its heavy-handed tactics, including a military quarantine of West Point, the largest slum in the capital, Monrovia.
While Ms. Johnson Sirleaf is internationally celebrated, her legacy at home remains disputed. In 2012, a fellow Nobel laureate, Leymah Gbowee, quit in frustration as the head of the Liberia’s reconciliation initiative and criticized Ms. Johnson Sirleaf for hiring her sons for high-level government posts and failing to tackle graft and corruption. Last month, her party expelled her and accused her of supporting Mr. Weah over his rival, Joseph Nyumah Boakai, her former vice president.
Ms. Johnson Sirleaf is credited with negotiating with the International Monetary Fund and World Bank to erase $4.6 billion worth of debt, and her government attracted commitments of $18 billion worth of investment during her first term.
But the challenges facing Liberia remain formidable. It remains one of the poorest countries in the world, and with commodities like rubber and iron ore fetching low prices on the international market, it is expected to encounter tougher economic times.