President Olusegun Obasanjo: Mr Obasanjo is a former military ruler and fought during the Biafran civil war of the 1960s. Imprisoned under the military regime of Gen Sani Abacha, he was released at the end of military rule and persuaded by Nigeria’s political elite to run for office. An evangelical Christian, Mr Obasanjo is a Yoruba, the main ethnic group in the south of the country. After eight years as president, his successor must come from the Muslim north according to an unwritten agreement amongst Nigeria’s political elites. During his eight years in office, Mr Obasanjo, who doubled as Nigeria’s official oil minister for eight years, started a programme of economic reforms that partly led to Nigeria writing down most of its $35bn external debt. Mr Obasanjo is due to stay on as an influential chairman in the ruling party after he steps down.

Umaru Yar’Adua: Mr Yar’Adua is the candidate for the ruling People’s Democratic Party (PDP). He is a governor from the northern state of Katsina and the younger brother of the late Shehu Musa Yar’Adua, Mr Obasanjo’s deputy during his time as military ruler. Once a socialist, Mr Yar’Adua joined the political mainstream in 1999 when he won governorship elections. His opponents say he is a puppet of Mr Obasanjo, though his supporters say he is a wily political operator capable of being his own man. Mr Yar’Adua health has been a major topic of debate in Nigeria. He has suffered from a chronic kidney condition, though he says he has since recovered. Mr Yar’Adua is a favourite to win, given the machinery, structures and influence of the PDP.