Dilma Rousseff, 62, is no stranger to the Planalto, the Brazilian president's office.
From 2005 until stepping down to run for office earlier this year, Ms Rousseff was President Lula's chief of staff, closely involved in the major decisions of his administration.
Lula has made it clear that the woman he calls the "mother of the PAC", his government's flagship economic development project, would be his choice as his successor.
Critics have dismissed Ms Rousseff as merely Lula's choice, a career civil servant never elected to public office.
She does suffer in direct comparison with the current president. With her somewhat dour image, she cannot compete with Lula's charisma and public-speaking skills.
Her background, born to a middle-class family and with a Bulgarian immigrant father, is also a far less compelling life story than Lula's rise from abject poverty to the highest office in the country.
But dig deeper and the toughness ascribed to her by colleagues - she is known for her short temper - becomes clearer.
As a student, she became involved in left-wing politics and joined the underground resistance to the military dictatorship that ruled Brazil from 1964 until 1985.
Ms Rousseff has said she was never actively involved in armed confrontation with the security forces, but she was jailed for almost three years and subjected to electric shocks.
Trained as an economist, Ms Rousseff was energy minister before being named as Lula's chief of staff.
It is clear that Lula's support has boosted her profile and her campaign to be the first female president of Latin America's biggest country.
Her challenge is to convince voters that she truly will be in charge if elected to the presidency.
Jose Serra, 68, has occupied some of the top political jobs in Brazil, including mayor of the biggest city, Sao Paulo, and governor of the state of Sao Paulo - the nation's biggest and wealthiest state.
From 1995-1996, Mr Serra was planning minister in President Fernando Henrique Cardoso's government.
He also occupied the health post in the Cardoso administration from 1998 to 2002, winning international plaudits for a range of programmes including an HIV/Aids treatment programme based on producing cheap replicas of patented medicines.
He was born into a family of poor Italian immigrants. At the time of the 1964 military coup, he was the head of the National Students' Union.
Forced into exile, he went first to Chile and then after the military coup there, he went to the US where he studied economics.
He returned to Brazil in 1977 as the country was taking its first steps towards the restoration of democracy.
Mr Serra was among the founders of the PSDB in 1988 and has served as a federal deputy and senator. He unsuccessfully ran against President Lula in 2002.
In 2004, he was elected mayor of Sao Paulo, a post he left to run successfully for the governorship of the state.
Mr Serra stood down as governor earlier in 2010 to stand as presidential candidate for his party.
Like Ms Rousseff, Mr Serra is not a great speaker but he will be hoping his long record in holding political office convinces voters the management of Brazil will be in capable hands.
Marina Silva who is running as the Green Party candidate is expected to come third but her share of the vote could have an impact on the outcome.
Ms Silva was President Lula's environment minister from January 2003 but she left the government in May 2008, citing difficulties in pursuing an environmental agenda.
In August that year, she also left Lula's Workers Party.
She was vocal in blaming the deforestation of the Amazon on Brazilian cattle ranchers and farmers.
The child of rubber-tappers from the Amazonian state of Acre, Ms Silva was illiterate until the age of 14.
She worked with the rainforest activist Chico Mendes, who was murdered in 1988, and she was appointed environment minister when Lula won the presidency in 2002.
Fonte: BBC News
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