Nigerian President Goodluck Jonathan and presidential candidate of the ruling People's Democratic Party (PDP) embraces leading opposition All Progressive Congress presidential candidate Mohammadu Buhari during a conference to promote non-violence att ~ STRINGER
Lagos - The two main candidates in the tense presidential election cut sharply different profiles: an ex-military ruler who cracked down on indiscipline and a zoologist rarely seen without his stylish fedora.
Incumbent Goodluck Jonathan, 57, is a Christian from the Niger Delta oil region in the south while Muhammadu Buhari, 72, is a Muslim from the north and a retired major general.
Their backgrounds in some ways mirror regional, ethnic and religious divisions in the country, with the north being mainly Muslim and the south predominately Christian.
But politics in a country with more than 300 ethnic groups and a population of 173 million is notoriously unpredictable, and support can shift in unforeseen ways.
The Boko Haram conflict, which has left more than 13,000 dead since 2009, has also played a major role in the campaign.
- Not his turn? -
An ethnic Ijaw from a family of canoe makers, Jonathan's rise to the top of his country's ruthless political world has been described as accidental.
Fortune certainly seems to have favoured Jonathan throughout his political career, as his first name would imply.
He became governor of his native Bayelsa state in 2005 after his predecessor was impeached over money-laundering charges in Britain.
The night he was nominated by his People's Democratic Party (PDP) as Umaru Yar'Adua's running mate before the 2007 polls, many Nigerians had never heard of him.
Some have argued he was chosen because he was seen as pliable and served to balance the ticket, representing the restive Niger Delta.
He was thrust into the presidency in 2010 following the death of Yar'Adua, a Muslim from the north, and ran in 2011 elections.
For many in Nigeria's north, it was not Jonathan's turn to be head of state.
His decision to run in 2011 violated an agreement within his PDP to rotate its candidate between the north and south every two terms.
Because Yar'Adua died before his first term was up, northern elites believed the presidency should have returned to their region.
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In the end, he ran and won handily - beating out Buhari - making him the first elected Ijaw president and the first from the Niger Delta.
- War Against Indiscipline -
As for Buhari, he has tried three times to become president since the return to civilian rule in 1999 - and failed on each occasion.
He was the country's military ruler from December 31, 1983 to August 27, 1985 after he ousted elected president Shehu Shagari.
He is seen as an anti-corruption figure but his regime in the 1980s was also accused of serious rights abuses.
His "War Against Indiscipline" sought to bring order to the country, but was seen as draconian.
In particular, the execution of three young men, found guilty retrospectively of drug trafficking triggered domestic and international outrage.
Critics of his regime were thrown in jail, among them Afro-beat legend Fela Kuti for an alleged currency violation but which critics said was politically motivated.
Buhari was also at the centre of a major diplomatic row with former colonial power Britain after attempting to smuggle Shagari's former adviser Umaru Dikko from London to Lagos.
Dikko, who had fled to the British capital after his boss' ouster, was found drugged in a crate at Stansted Airport.
In the campaign ahead of this year's election, Buhari, an ethnic Fulani, has sought to distance himself from his previous military rule, saying he would serve as a civilian leader within the bounds of democracy.
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