Former Brazilian leader Luiz Inácio Lula da Silva has launched his campaign for October's presidential election.
At a rally, the left-winger called on Brazilians to support him in defending the country's democracy from the far-right President Jair Bolsonaro.
Lula led the country for eight years from 2003, but was later convicted of corruption and jailed before having the judgment overturned last year.
The rally was called a "pre-launch" as official campaigning begins in August.
Lula's campaign pledges to "join democrats of all political positions, classes, races and religious beliefs".
The 76-year-old told supporters that the current situation in the country "forces us to overcome our differences and build an alternative path to the incompetence and authoritarianism that governs us".
"I'm jumping back into the fight," he told a cheering crowd in São Paulo on Saturday.
Lula, who governed Brazil between 2003 and 2010, is a towering figure in left-wing politics in Brazil and beyond. His government helped lift tens of millions of people from poverty.
But in 2018 he was the most senior politician to be convicted as part of an investigation into a huge bribery scandal, known as "Operation Car Wash".
After his conviction and 12-year jail sentence, Lula was banned from the presidential race in 2018.
But last year, a Supreme Court judge annulled his corruption convictions, ruling that a biased judge who looked at Lula's case had compromised his right to a fair trial.
Earlier this year, Mr Bolsonaro said that Lula's return to presidency would be like "the return of a criminal to the crime scene".
There are growing fears that, if Lula wins the October elections, Mr Bolsonaro might not accept defeat as he has repeatedly questioned Brazil's electronic voting system.
Lula has picked the centrist former governor of São Paulo, Geraldo Alckmin as his running mate for vice-president. Mr Alckmin's more moderate political stance is expected to attract voters who are unhappy with President Bolsonaro's administration, but are also wary of Lula's politics.
Mr Alckmin, who stood against Lula in the 2006 presidential elections, thanked Lula for his trust and said he is proud of their alliance.
Recent opinion polls show that Lula has a comfortable advantage over his rival.
President Bolsonaro has faced pressure from the public over his handling of the Covid-19 pandemic, but his popularity has increased after a boost in his government's welfare spending.