|Muhammadu Buhari is former military ruler and candidate for the Congress for Progressive Change [Reuters]
Muhammadu Buhari, Nigeria's former military ruler, is a Muslim from the country's north and seen as the main challenger to Goodluck Jonathan, a Christian from the south.
The former leader, who ruled from December 1983 to August 1985, also has a reputation as a fierce anti-corruption figure, after he jailed hundreds of politicians, officials and businessmen during his reign.
Born in December 1942, he is the country's oldest presidential candidate. After joining the military Buhari entered politics in 1976 as a minister under Olusegun Obasanjo, the former military ruler. He was picked to lead the country by military officers after an almost bloodless coup in 1983.
His rule was characterised by strict austerity measures, the jailing of politicians on corruption charges and the execution of drug traffickers and armed robbers. Some have criticised this period for human rights abuses and heavy-handedness, but others say it helped fight corruption in Nigeria.
However, in August 1985, Buhari was overthrown in another coup led by general Ibrahim Babangida, and jailed for 40 months.
Since then he has remained active in politics, unsuccessfully running for president in the 2003 and 2007 elections.
He has been viewed with suspicion by Christians in the south after allegations that he had a radical Islamist agenda.
But this year he may benefit from regional divisions, with many Muslims angered by the campaign of Jonathan, which breaks a pact within the ruling party that says the presidency must rotate candidates between the north and the south.
Buhari's reputation as a disciplinarian and a popular perception that he is cleaner than many in the political elite also make him the main opposition candidate to Jonathan.