Depending on the day and which negative political ads have recently aired on Mexican television, one of two top candidates for president will take a slim lead: Andres Manuel Lopez Obrador, the Democratic Revolution Party's liberal, leftist hopeful, and Conservative Felipe Calderon, backed by President Vicente Fox and a loyal follower since childhood of his National Action Party, or PAN.

While Lopez Obrador touts himself as an outspoken champion for the poor, the more subdued Calderon heralds job growth and crime reduction as the answer to Mexico's problems.

Calderon's father, who helped found the conservative PAN in the 1930s, encouraged his sons to work on his campaigns and to help push the democratic movement in Mexico. Calderon officially joined PAN on his 18th birthday and later became leader of its youth movement, the Arizona Daily Star reported. At the age of 25 he won a seat on the Mexico City assembly and later a seat in the House. A failed bid for the governorship of his home state of Michoacan did little to slow his rise.

In 1996, at the age of 33, Calderon was chosen to lead PAN. He helped steer the party to victory in 2000 when Fox won the presidency, ending 71 years of the Institutional Revolutionary Party's authoritarian control of Mexican politics.

As prospects for Fox's win looked hopeful, Calderon took a break from the campaign, electing to spend time in the United States with his family. From 1999 to 2000 he moved to Massachusetts, where he spent a year at Harvard University's Kennedy School of Government.

"I had two children born while I was party president, and I have been away a lot," Calderon told the Washington Post. "My second son was born at 4 a.m., and at 6 a.m. I got a call that the governor of Baja, California had died. I left the hospital and went straight to Baja."

Since Fox's victory, despite Calderon's fierce loyalty to his party, the two men have had their differences. Fox appointed Calderon energy secretary in 2003, but Calderon later resigned after Fox accused him of launching a campaign for president while Fox was still in office, the Arizona Star Daily reported.

In the lead-up to the 2006 election however, the two men appear to have settled their differences. Fox has been accused by other candidates of illegally campaigning on Calderon's behalf -- the law says presidents may not campaign for their replacements.

And, the former lawyer and self-professed Panista, or PAN loyalist, has fashioned his campaign based partly on Fox's record in office.

Calderon has said that while Fox's policies have moved the country in the right direction, as president he would further that progress in areas of economic development and free market trade -- a message comforting to his largely middle-class base.

"I want to keep Mexico on the path of modernization and economic growth," Calderon said in a Washington Post forum in June 2006. "We need to improve the competitiveness of enterprises here in order to improve the performance of the economy and to get higher growth rates."

Calderon's solution to the U.S. immigration problem is to create more jobs in Mexico so Mexicans won't have to migrate North, legally or illegally.

While the candidate appears to be a solemn and religious statesman, his opponents paint a seedier picture. Lopez Obrador has accused the former energy minister of illegally awarding his brother-in-law contracts while he served in Fox's administration. Calderon has denied the accusations, but has retaliated, painting his rival in nasty campaign ads as a wildcard danger to the Mexican public.

"[Obrador] is like a thief calling someone else a thief," he told the Post.

"He will take the country to a new economic crisis," he added. "He believes that laws are a relative [concept], and they are subject to his concept of justice. Several times he has said that if a law is not just, he will not apply that law."

At 43, Calderon is the youngest of the presidential candidates. The father of three, he is married to Mexican lawyer and congresswoman, Margarita Zavala.

-- Compiled by Kristina Nwazota for the Online NewsHour