Atiku Abubakar, 76, is standing for the Peoples Democratic Party, the largest opposition party (PDP).
He has previously run for president five times, all of which he has lost.
Most of his career has been in the halls of power, having served as a top civil servant, vice-president under Olusegun Obasanjo and a renowned businessman.
He has built his campaign on his experience as Mr. Obasanjo’s deputy, which included major reforms in the telecoms, pension, and banking sectors.
He, like many of the other contenders, has been accused of favoritism and corruption, which he rejects.
Some in his party have expressed dissatisfaction with his candidacy, claiming that it is time for a southerner to be president after nearly eight years under President Muhammadu Buhari, who is from northern Nigeria, like Mr Atiku.
