By Senan Murray
BBC News, Abuja
A founding member of Nigeria's ruling People's Democratic Party, Vice-President Atiku Abubakar, 60, was forced out of the party after a bitter feud with President Olusegun Obasanjo.
In a probe ordered by Mr Obasanjo, the vice-president was accused of diverting $125m from a public development trust fund into his personal businesses.
Mr Abubakar says his wealth comes from wise investments and luck
Although Mr Abubakar has denied the allegations and has hit back at President Obasanjo with counter-allegations of corruption, some of the mud may have stuck.
Mr Abubakar is still faced with the difficult task of convincing Nigerian voters that 20 years in the customs service is enough to make one a multi-millionaire, with business interests in oil, media, publishing and education.
He owns the high-profile ABTI American University of Nigeria in his north-eastern Adamawa State.
His oil services company Intels Nigeria Limited operates in Angola, Equatorial Guinea, Gabon and Sao Tome and Principe.
In his most explicit comment yet on the source of his wealth, Mr Abubakar says, in a newly published biography, that he became wealthy "through wise investments, hard work and sheer luck of being at the right place at the right time."
But the anti-graft agency, the Economic and Financial Crimes Commission, which has probed Mr Abubakar's handling of the Petroleum Development Trust Fund (PTDF), does not believe him.
The vice-president's legal battles could keep him distracted while President Obasanjo concentrates on trying to install the PDP's Umaru Musa Yar'Adua as his successor when he steps down in May.
A Lagos High Court has voided two reports accusing Mr Abubakar of corruption - but appearances before the Senate and in court could still see him ruled out of contention for the presidency.
Now running on the opposition Action Congress ticket, Mr Abubakar still has to overcome the ANPP's Muhammadu Buhari if he is to compete in April's elections after an electoral pact between the two parties.
He has four wives and several children but no living brothers or sisters.
"He is a humble, kind-hearted family man who does not forget his friends," his spokesman, Garba Shehu told the BBC News website.
But others see Mr Abubakar differently - as a shrewd politician who does not hesitate to spend huge amounts of money to achieve his political ends.
He says his political role model is former US President Bill Clinton.
"Clinton is just a fantastic politician. You could tell that he loves politics and I just love politics."
Mr Abubakar had been hoping that the campaign for "power shift" - the idea that it is the north's turn to hold power after Mr Obasanjo, a southerner - would work in his favour.
But like Mr Buhari and the ruling PDP's Mr Yar'Adua, Mr Abubakar is a Fulani Muslim, so what he had hoped would be his support base has been diluted.
David and Goliath
He sees himself as "the symbol of democracy in Nigeria" because of his public opposition to attempts to change the constitution to let President Obasanjo stand for a third term in office.
Mr Abubakar's supporters say they have been victimised
That stance has put Mr Abubakar in the good books of many Nigerians, but may not translate to votes in April because some feel he was mainly motivated by a desire to take Mr Obasanjo's job.
Furthermore, those people who want change after eight years of Mr Obasanjo will hesitate to back the man who was second-in-command for all that time.
However, Mr Abubakar's feud with President Obasanjo is fast becoming a sort of David and Goliath story with many would-be voters empathising with the vice-president whom they see as a persecuted man.
"The president is using state might to fight Atiku and a lot of people feel that the president's viciousness towards his deputy, who is David in this case, is really uncalled for," says political analyst Adamu Hamza.
And if money alone can win votes - and it does tend to win votes in Nigeria - then Mr Abubakar may well be Nigeria's president-in-waiting.