Andres Manuel Lopez Obrador, the former mayor of Mexico City and member of the left-leaning Party of the Democratic Revolution (PRD), is fighting for his last chance at the country's top post. This time he is ready to defend the vote he called fraudulent six years ago.

Obrador's election as mayor of Mexico City in 2000 disrupted the country's political class. While most governors, members of congress and high-ranking bureaucrats started their days at luxury gyms and fancy restaurants, beginning work only after 11am, Obrador, now 58, began his days at 5am with a security meeting and a daily press conference at 6am.

By the time that others - including the president - were just starting to read the newspapers, Obrador was already ahead of the game, making headlines. That's how he announced cuts to the salaries of high-ranking public officials, including himself.

With no armoured cars and dozens of bodyguards - unlike predecessors from the long-ruling Institutional Revolutionary Party (PRI) - he started driving a small sedan.

It was no surprise that Obrador became a potential favourite in the presidential race in 2006.

'Populist' candidate

Hundreds of citizens, many from other states over which Obrador had no jurisdiction, started to camp outside his office, waiting for the mayor to appear before sunrise to deliver him letters requesting help to deal with the corrupt bureaucracy, to ask for a job, or request free medical attention denied in other states.

As mayor, he financed public works projects by cutting down on about $2bn of what his supporters considered to be corruption and unnecessary public spending in his first year in office. The road seemed paved for the popular mayor to conquer the presidency. That's when the political system, he claims, began the attacks.

He was labelled "populist" for using some of the savings to provide pensions to the elderly and expand a decaying public health system.

Vicente Fox, who was elected president the same year Obrador became mayor, staged a legal battle against Obrador to strip him of immunity to face charges for having expropriated a small stretch of land to build road access to a hospital.

Public support for Obrador was strong, and Fox had to reverse the legal battle. A few months before election day in July 2006, Obrador was 10 points ahead in the polls and seemed a likely winner, but he made a critical mistake: he decided to skip a presidential debate.

The right-wing National Action Party (PAN) launched a successful negative campaign, calling Obrador a threat, and linking him to Venezuelan President Hugo Chavez.

Obrador was further weakened when videotapes emerged depicting members of Obrador's inner circle taking millions in cash from a businessman.

Rumors spread that Obrador was going to seize private property to give it away to the poor. His once-comfortable lead evaporated.

Election day

A few days before the vote - held on a pay day - thousands of business owners called their employees for a "meditation talk". Paychecks were delivered along with a speech crafted by the leadership of business groups, critics say. Workers - many of whom were in debt for homes and appliances - were told that if Obrador were elected, companies would remove their investments from Mexico. Many analysts and historians believe this strategy had an effect on the vote.

In the official outcome, Obrador lost to PAN's nominee Felipe Calderon by 0.55 per cent.

Obrador's supporters accused Calderon of fraud, staging massive protests on Mexico City's largest avenue for a couple of months. Yet many of Obrador's supporters turned against him for making what they said was a huge tantrum.

Obrador called himself the "legitimate president" and began touring the country, preparing a comeback. He has since moderated his speech and is now trying to win votes from the middle classes who turned their backs on him in 2006. He remains second in most polls, although a students' movement is said to be bolstering his support, while eroding the lead of frontrunner Enrique Pena Nieto, who enjoys the support of the big television networks.

He is one of the last of a generation of Mexican leftists who came from inside the old system and tried to change it with no success - so far. If he loses his bid for the presidency this time, he will most probably retire from politics, leaving room for a new generation.

His party is likely to retain control of the Mexico City government, with polls indicating roughly 60 per cent support for the PRD.