Muhammadu Buhari is seeking re-election next year and he made Nigerian political history as the first opposition candidate to defeat a sitting president at the ballot box.
But since his election just over three years ago, the former military ruler has faced persistent rumours of ill-health, criticism of his handling of the economy and security and questions over his campaign to root out corruption.
The presidency says the 75-year-old leader would seek a second straight term.
“Victory is sure by the grace of God and together we must continue to sanitise Nigeria’s political environment,” he said.
During the 2015 election campaign, the People’s Democratic Party (PDP) of his opponent Goodluck Jonathan claimed the rapier-thin Buhari was “mortally ill” from prostate cancer.
Buhari and his All Progressives Congress (APC) party dismissed the assertion as another smear intended to portray him as unfit for office.
But health concerns have been persistent throughout his tenure. In June 2016, Buhari flew to London for treatment of what aides called a persistent inner ear infection and returned there to see doctors in early 2017. Aides had to counter persistent rumours that he was seriously ill and even dead.
Another problem facing Buhari has been the economy. Nigeria slipped into recession in 2016 with sky-high inflation, which has been steadily coming down.
On the security front, Buhari declared in December 2015 that Boko Haram’s jihadists who once tried to blow him up were “technically” defeated.
But the group still stages deadly attacks on both military targets and civilians and the insurgency has spilled over into neighbouring countries.
Pro-Biafra groups wanting secession in the southeast are resurgent and deadly clashes have resumed between herdsmen and farmers in central states.
On corruption, there have been several headline-making arrests but no high-profile convictions and it is unclear whether Buhari’s zeal for transparency and accountability extends to the wider political establishment.
Buhari’s 2015 election win – after three failed attempts in a country where victory for the incumbent had been taken for granted – was a rare opportunity for Nigeria to change course.
His pledge to give his “strength, commitment, sweat and toil in the service of the people” raised hopes for an end to decades of rampant cronyism, corruption and impunity.