Bola Tinubu, declared the winner on Wednesday in the presidential election, has boasted of making the careers of major politicians. Now he has to deliver for a divided country facing multiple emergencies.

Peter Obi was until recently a secondary player in Nigerian politics. By switching parties and appealing to the digitally savvy, he overturned the old order.

Eritrean troops have been accused of war crimes in the northern Tigray region just weeks before a peace agreement was signed last year.

Despite scandal and controversy, David Mabuza remained in office for five years, only leaving once he had lost power within the governing African National Congress party.

Mr. Tinubu, a former governor of Lagos and the ruling party candidate, campaigned using the slogan “It’s my turn.” He promised to address widespread insecurity and economic woes, but he faced concerns about his fitness for office.