The 86-year-old Senegalese faces corruption and money-laundering charges linked to the Russian doping scandal.

Diack was investigated by French authorities for four years over claims he took payments of more than 3m euros to cover up cheating.

He has been under house arrest in Paris since November 2015.

The landmark trial is scheduled to run for the next two weeks.

Diack denies the charges, but if found guilty he could face up to 10 years in jail.

Background

Previously one of the most influential figures in world sport, Diack was president of the International Association of Athletics' Federations (now World Athletics), for 16 years until he was replaced by Britain's Lord Coe in August 2015.

At the time Coe described Diack as the "spiritual leader of our sport", though he has since distanced himself from those comments.

Three months later details emerged of Diack's alleged involvement in a conspiracy to bury positive drug tests by Russia dopers in return for money.

His arrest plunged the IAAF into an unprecedented scandal, and has done huge damage to athletics' credibility.

In January 2016, a report by the World Anti-Doping Agency concluded that Diack was "responsible for organising and enabling the conspiracy and corruption that took place in the IAAF".

It is also alleged by French prosecutors that Diack - a former mayor of Dakar in Senegal - used some of the payments channelled through the IAAF's base in Monaco to fund political campaigns in his native homeland.

The five co-defendants

Also appearing in court will be Diack's ex-legal aide Habib Cisse (who faces a charge of complicity in corruption) and former anti-doping boss Gabriel Dolle (corruption) for their roles in the alleged conspiracy.

Diack's son Papa Massata Diack - who was banned for life from athletics in 2016 - is expected to be tried in his absence having been accused of playing a central role in the network of alleged corruption. He is charged with corruption, money laundering, concealment and breach of trust.

The marketing executive, who handled valuable rights for the IAAF, is believed to be in Senegal having refused to leave the country despite two international arrest warrants. The country's authorities have said they will not extradite him.

In 2015 he told BBC Sport that he "totally rejects" accusations he had any role in extortion or bribery via 'Black Tidings' - a now-defunct Singapore-based firm linked to him.

Former Russian athletics chief and IAAF treasurer Valentin Balakhnichev (corruption and money laundering) and Russia's ex-middle distance coach Alexei Melnikov (corruption) will also be tried in their absence.

All six defendants strenuously deny the charges. The trial will be overseen by judge Rose-Marie Hunault.

Proceedings are expected to focus on the case of Liliya Shobukhova, the 2010 London marathon winner. In 2016, the IAAF banned Diack Jr, Balakhnichev and Melnikov after finding that they had conspired to "blackmail" the Russian athlete to cover up her doping violations by her paying them "bribes" of about £435,000.

All three had their appeals against their life bans rejected by the Court of Arbitration for Sport in August 2017.

Prosecutors from France's Parquet National Financier (PNF) have also been investigating allegations that Diack Snr received bribes for his votes in several bidding contests for high-profile sports events, including the Rio 2016 and Tokyo 2020 Olympics. The former International Olympic Committee member is claimed to have controlled the votes of several African colleagues.

The scandal the Diack trial is directly linked to, resulted in Russian athletes being banned from the Rio 2016 Olympics. The country's whole team was then banned from the 2018 Winter Games and faces the same punishment for next year's Tokyo Olympics.