President Goodluck Jonathan, flanked by National Emergency Management Agency (NEMA), Muhammad Sani Sidi (at his right) and Governor of Borno State Kashim Shettima at (center of the picture), gestures as he speaks to internal displaced people from Bag ~ OLATUNJI OMIRIN
Abuja - Nigerian President Goodluck Jonathan and Vice President Namadi Sambo are in a tight contest for Saturday's election with main opposition candidate Muhammadu Buhari and his running mate, Yemi Osinbajo.
The vote is widely expected to be the closest presidential poll Africa's most populous nation and biggest economy has seen since it returned to civilian rule in 1999.
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In all, there are 14 presidential candidates but Jonathan and Buhari are well ahead of the rest.
Here are details on the main presidential and vice presidential aspirants of their parties.
People's Democratic Party (PDP) Presidential candidate: Goodluck Jonathan
Goodluck Ebele Jonathan was born in the Niger Delta in November 1957 to a family of canoe makers. He studied zoology and worked as an education inspector, lecturer and environmental protection officer before going into politics in 1998.
Usually dressed in his trademark fedora hat and traditional caftan-like attire, he has a PhD in zoology. Jonathan won election in 1999 as deputy governor of Bayelsa, one of three main states in the oil-producing Niger Delta, as a member of the PDP. He became state governor in 2005, then vice president in 2007 alongside President Umaru Yar'Adua.
Jonathan was sworn in as president, vowing to fight corruption, on May 6, 2010, a day after Yar'Adua died.
His 2011 election upset northern elites due to an informal pact within the PDP that power should rotate between the mostly Muslim north and the largely Christian south every two terms.
Jonathan's administration has been dogged by several corruption scandals in the oil sector. In early 2013, the president dismissed the then central bank governor Lamido Sanusi after the latter accused the state oil company of failing to remit billions of dollars of oil revenues it owed the state.
The Christian southerner has been criticised for failing to tackle a six-year Boko Haram insurgency, during which the militant group killed thousands in its attempt to set up an Islamic state in northeast Nigeria, and kidnapped hundreds.
Vice presidential candidate: Namadi Sambo
Mohammed Namadi Sambo was born in August 1954 in northern Kaduna state. Jonathan will hope his Muslim running mate will attract votes in the north where the president is least popular.
Sambo is a qualified architect. He held positions in the Ministry of Works, Transport and Housing in the 1980s, left to pursue private practice in the 1990s before returning to politics as governor of Kaduna state in 2007.
His main achievement as governor was on security, a major problem in Kaduna which has suffered from sectarian clashes.
All Progressives Congress (APC) Presidential candidate: Muhammadu Buhari
Buhari, born in December 1942, was military ruler of Nigeria between December 1983 and August 1985. He was also an unsuccessful candidate in the 2003 and 2011 elections.
A major general, he was selected to lead the country by military officers after an almost bloodless New Year's eve coup in 1983 ended Nigeria's second attempt at democracy.
His iron-fisted administration is remembered for the jailing of politicians for corruption and executing of drug traffickers.
Buhari himself was overthrown in a 1985 coup. His reputation as a disciplinarian, and a popular perception that he is cleaner than many in the political elite, has played well with voters fed up with worsening corruption.
The bloody Boko Haram insurgency has made security a major campaign issue for Buhari. He points to his achievements as a military ruler against Chadian militia.
Vice presidential candidate: Yemi Osinbajo
Osinbajo, a southern lawyer, was announced as Buhari's running mate in December 2014.
He is also a Christian pastor, a move aimed at wooing Christians who might be unhappy with a Muslim northern presidential candidate, a pattern in Nigerian elections in which aspirants try to balance the two religions.
The selection of Osinbajo as a vice presidential candidate is also likely to be an attempt to win over voters in the southwest, where he is from, seen as the major swing block.