Al Jazeera looks at the two vastly different characters aiming to be the president of South Africa's ruling African National Congress.
Jacob Zuma, deputy leader of the African National Congress (ANC)
Zuma, born in the KwaZulu-Natal province, joined the ANC in 1959 and became an active member of its militant wing in 1962. He was arrested in 1963, convicted of conspiring to overthrow the government and sentenced to 10 years in prison on Robben Island.
Thabo Mbeki, the current preisdent, chose Zuma - an ethnic Zulu - as deputy president in 1999, in part in recognition of the role he had played in ending violence between members of the ANC and members of the main Zulu party in the KwaZulu-Natal province.
Mbeki fired Zuma as his deputy in June 2005 after Zuma's financial adviser was convicted of fraud and bribery in a multi billion dollar arms deal. Zuma remained deputy president of the ANC, under Mbeki.
Charges against Zuma alleging he was aware of his adviser's efforts to elicit a $70,000 bribe for him to deflect investigations into the deal were later withdrawn.
Zuma was acquitted last year of raping a family friend, but he had described the sex as consensual.
He outraged Aids activists and prompted public questions about his leadership ability and judgment when he testified during the trial he had unprotected sex with the HIV-positive woman and believed taking a shower afterward would protect him from Aids.
After the rape and corruption charges, few thought Zuma had a political career left. But he continued to have support and be seen as a defender of the poor and downtrodden and an antidote to the aloof and intellectual Mbeki.
The country's largest trade union federation, the South African Communist Party and the left-wing ANC Youth League have rallied behind Zuma, maintaining he was the victim of a plot to stop him from becoming president.
Thabo Mbeki, president of South Africa
A member of one of the ANC's most powerful families, Mbeki, 65, was sent to study in Britain during the apartheid years.
First elected in 1999 to succeed Nelson Mandela as South Africa's second black president, Mbeki has presided over an economic boom.
A long-time member of the ANC and son of a senior party leader, Mbeki joined the ANC Youth League at 14 and became active in student politics.
He backed the ANC's armed campaign against apartheid and spent years lobbying against apartheid across the world.
He has been credited with South Africa's economic growth and worked to mediate in conflicts in the Ivory Coast, Sudan and elsewhere on the African continent.
But while he has been aclaimed abroad he has attracted inreasing criticism at home.
Critics say he has undermined South Africa's democratic credentials by using state institutions to purge opponents, something he denies..
Activists say he has failed to lead the campaign against an epidemic that kills at least 900 people a day in South Africa.
Some say his market-oriented economic policies have been too slow to pull the black majority out of poverty.
In addition, Mbeki has been repeatedly accused of doing too little to stop crime in a country suffering from one of the world's highest rates of murder and rape.