The BBC News website's Senan Murray profiles the strongest presidential candidates in Nigeria's election on 21 April.
Umaru Musa Yar'Adua, 55, PDP
The governing People's Democratic Party (PDP) candidate is a little known Muslim former polytechnic teacher, Umaru Musa Yar'Adua.
He is not particularly popular among Hausas who make up a majority in Nigeria's Muslim north, but this relatively colourless politician was President Olusegun Obasanjo's "anointed" successor.
This proved crucial in him securing the nomination and makes him clear favourite to win the election - especially after the huge PDP successes in the state elections on 14 April. If he does so he will be Nigeria's first university-educated leader for some 40 years.
He is the current governor of Katsina State and one of the few serving governors not being investigated for corruption.
His prudent management of money is what is believed to have endeared him to Mr Obasanjo.
His late elder brother, Gen Shehu Musa Yar'Adua was President Obasanjo's deputy when he was Nigeria's military ruler between 1976 and 1979.
Taciturn with some leftist leanings, Mr Yar'Adua is famous for his humility.
On more than one occasion, he has ignored the advice of aides and bodyguards by walking alone to a tobacco kiosk to buy a single cigarette.
His critics describe him as slightly totalitarian.
His running mate, Goodluck Jonathan is a southern Christian governor, which is intended to ensure he attracts enough votes across the country to avoid the need for a second round.
Muhammadu Buhari, 64, ANPP
Former military ruler Muhammadu Buhari is the candidate for the main opposition party, the All Nigeria People's Party (ANPP).
Although he lost to President Obasanjo in the 2003 elections, Mr Buhari appears undeterred in his quest to be an elected head of state.
At its September convention, the party made it clear to the former military ruler that he was no longer in charge.
Mr Buhari had hoped to strengthen his influence in the ANPP by backing his supporters for key positions in the party's national executive committee.
But the ANPP governors, who are the party's major financiers, rejected Mr Buhari's candidates, effectively leaving him alone and powerless.
However, when the party met in Abuja to choose its candidate, six of the seven nominees stood aside leaving the road clear for him.
Mr Buhari, who like Mr Yar'Adua is from Katsina State, enjoys some support in the Muslim north and is seen by many Nigerians as a disciplined and prudent man.
But many Christians worry about his strong religious views.
The ANPP and Action Congress (AC) did agree to unite behind one candidate, but this fell by the wayside. His weak party organisation means Mr Buhari has a mountain to climb.
Vice-President Atiku Abubakar, 60, AC
A founding member of the PDP, Vice-President Atiku Abubakar was suspended from the party after he was accused of diverting $125m to personal businesses.
Mr Abubakar denies the accusation but his bitter feud with President Obasanjo led to him becoming the candidate of the opposition Action Congress.
As well as throwing up a potential constitutional crisis by switching political sides while serving as vice-president, Mr Abubakar has faced numerous legal battles to contend with that threatened his participation in the polls.
A Lagos High Court has voided two reports accusing Mr Abubakar of corruption - but with Inec excluding him from the list, he was in court until days before the presidential polls .
His triumph in the Supreme Court five days before the polls, means he can compete, but it remains unclear how his name will appear on the ballots in time.
A Fulani Muslim, he enjoys wide backing in the predominantly Muslim north, but the only state governorship it won on 14 April polls was in Lagos in the south-west.
He 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 all the main candidates so far are northerners, diluting one of his key appeals.
However, his public opposition to attempts to change the constitution to let President Obasanjo stand for a third term in office has put Mr Abubakar in the good books of many Nigerians.
Chukwuemeka Odumegwu Ojukwu, 73, APGA faction
A reformed warlord, Chukwuemeka Odumegwu Ojukwu led the failed Biafra secession move that plunged Nigeria into a three-year civil war that ended in 1970.
Mr Ojukwu is a cult figure among his Igbo people who see him as an emancipator because of his role in the war.
But that is about where his influence ends.
Although he has just been given his party's presidential ticket on a platter, it is only from a faction of the All Progressive Grand Alliance (APGA), whose field of influence does not go beyond south-eastern Nigeria.
Orji Uzor Kalu, Progressive Peoples Alliance (PPA)
The multi-millionaire governor of Abia State, is the presidential candidate for the Progressive Peoples Alliance - a new party formed by PDP dissenters in southeastern Nigeria.
Prof. Patrick Utomi, African Democratic Congress (ADC)
Prof Patrick Utomi's ADC party is composed mainly of younger-generation intellectuals. It is said to have a strong appeal among Nigerians in the diaspora.