Sepp Blatter and Michel Platini, once the most powerful duo in world soccer, are on trial facing charges of corruption. Here's everything you need to know.

Swiss sports administrator Blatter, 86, joined FIFA in 1975 as technical director. Six years later, he was named general secretary before his election as president in 1998.

Despite a controversial reign, Blatter continued to be re-elected time and again, remaining in the role for 17 years.

Platini, 66, joined UEFA in 1998 after an extremely successful playing career, which saw him win three Ballons d'Or, and a brief spell as the head coach of the French national team.

After rising through the organization's ranks, he was elected as UEFA president in 2007 and held the role until 2015.

In 2015, FIFA found itself at the heart of an FBI investigation into claims of corruption, financial misconduct, bribery, and vote-rigging.

Following a raid on a luxury hotel in Zurich in May of that year, seven FIFA executives were arrested by the US Department of Justice. Four others were arrested at separate locations at later dates.

Blatter subsequently resigned from his post, and Platini was tipped to take over.

However, in September, the Swiss Office of the Attorney General (OAG) then announced it was investigating Blatter in relation to payments made to Platini.

In December, FIFA's Ethics Committee banned both Blatter and Platini from soccer for eight years. Platini's ban was later reduced to four years and Blatter's to six, but in 2021 Blatter was then given a further six-year ban after a probe into unlawful bonus payments.

In November 2021, Blatter and Platini were charged with fraud and other offenses in Switzerland, six years after the OAG launched its investigation into the pair.

Blatter is accused of "fraud, in the alternative of misappropriation, in the further alternative of criminal mismanagement as well as of forgery of a document."

Platini is accused of fraud, misappropriation, participating in criminal mismanagement as an accomplice, and forgery of a document.

The charges relate to a 2011 payment of $2 million, authorized by Blatter, to Platini.

The OAG investigation found that Platini had demanded the payment for his work as a FIFA consultant between 1998 and 2002. Platini had agreed at the time to an annual salary for the work, approved by Blatter, of around $300,000. However amid financial problems in the early 2000s, FIFA was unable pay Platini in full. He did not pursue the outstanding debt until January 2011, when he sent FIFA an invoice and was paid 10 days later.

On Wednesday, June 8, the first day of the trial at the Swiss Federal Criminal Court, the hearings ground to halt when Blatter said he was too ill to testify.

"I am having difficulty breathing," the 85-year-old told the court.

He returned to make his testimony Thursday, when he told the court that the money transferred to Platini followed a "gentleman's agreement" between the pair. He denied the payment was unlawful.

"It was an agreement between two sportsmen," Blatter said. "I found nothing wrong with that."

The trial is scheduled to last for 11 days and reach its conclusion on June 22, with a verdict expected on July 8.

If found guilty, Blatter and Platini face up to five years in jail.