The trial of Rui Pinto, the man behind the "Football Leaks" that exposed shady dealings by leading clubs, players and agents, begins on Friday in Lisbon, with the hacker facing 90 charges.
The accusations include attempted blackmail, computer hacking, breach of correspondence and data theft.
"I hope to be acquitted because I am a whistleblower and I acted in good faith," the 31-year-old hacker told Der Spiegel, one of the publications that published the material from the Football Leaks in 2016.
But the charges include stealing money from a Cayman Islands account and trying to extort money from a Portuguese-based football agency.
After leaking the hacked documents, Rui Pinto fled Portugal and took refuge in Hungary, where he had spent a year as an Erasmus scholar. He spent four years there before being tracked down and extradited by Portugal in March 2019. On his return he was put in pre-trial detention for a year.
He was released to house arrest after cooperating with Portuguese prosecutors by giving them access to a mass of encrypted unpublished documents.
He is in a witness protection programme in exchange for his collaboration on other cases.
In March, the Portuguese judiciary also launched an investigation targeting the country's main clubs and the powerful Portuguese agent Jorge Mendes, due to suspicions of tax evasion in player transfers.
Pinto, a self-taught hacker, allegedly obtained this information by illegally accessing the computer systems of a host of clubs, agents, lawyers and investment funds.
Football Leaks exposed possible tax evasion, fraud, corruption and other misdeeds involving star players and club managers. The information has led to the opening of legal proceedings in France, Spain, Belgium and Switzerland.
The revelations caused tax problems for Cristiano Ronaldo linked to his move to Real Madrid and exposed Paris Saint-Germain's youth team racial quotas and deals between UEFA and PSG and Manchester City over Financial Fair Play.
Pinto has also revealed that he was also behind the "Luanda Leaks", an investigation into the fraudulent origin of the fortune of billionaire Isabel dos Santos, daughter of former Angolan president Jose Eduardo dos Santos.
Portuguese media have reported that Rui Pinto is behind the publication of a series of e-mails implicating Benfica, the most popular soccer club in Portugal, in corruption and tax evasion.
His lawyers insist he is "a very important European whistleblower" and plan to call 45 witnesses, including Edward Snowden, a former employee of the American intelligence charged with espionage, and the former French financial judge Eva Joly.
- 'I'm a whistleblower' -
Yet the charge that led to his extradition is attempted blackmail of businessman Nelio Lucas, the Portuguese who manages Doyen Sports, on behalf of a group of Kazakh-Turkish oligarchs.
Pinto allegedly asked for up to one million euros ($1.08 million) in exchange for not publishing documents he had obtained illegally.
"I regret having made contact with Nelio Lucas. I was naive at the time," he told Der Spiegel, saying he quickly dropped the demand for money.
He has said that he wanted to uncover the seedy underbelly of the "dishonest soccer industry".
His first successful hack, at the age of 23, involved stealing 300,000 euros from a bank in the Cayman Islands. He denies the charge of theft and says he kept data showing how the Cayman Islands were being used for "money laundering and tax evasion".
Pinto supports Porto and is from a suburb of the city. He is a small, youthful-looking man with spiky brown hair, described by his relatives as "sociable and cheerful".
He studied history and worked in his father's antiques business.
"I'm ready to fight to show everyone that I'm a whistleblower," he told Der Spiegel.
The case, Pinto said, "will be something like David against Goliath, because it will be me and my lawyers against the powerful and obscure interests of Portuguese society."