Lula is accused of influence peddling, starting in 2008 and continuing long after his presidency into 2015.
On Wednesday he is due to appear before Brazil's top anti-corruption judge, Sergio Moro, to face charges that he was given a luxury apartment as a bribe.
The case is part of a much wider corruption probe, dubbed "Car Wash," headed by Moro, which is unravelling a huge web of bribery by Brazilian executives to secure lucrative contracts with government companies such as the Petrobras state oil giant.
Although Lula currently leads in opinion polls, his legal problems mean he has a steep path to climb. If a conviction were upheld he would be barred from running for office again and could be imprisoned.
He denies involvement in any of the alleged schemes.
Prosecutors allege that OAS, a major construction company, paid Lula 3.7 million reais ($1.16 million) out of 87.6 million reais in total to politicians and officials.
Lula is accused of receiving this in the form of a seaside triplex apartment near his home city of Sao Paulo while he was president in 2009. The case partly rests on testimony from former OAS head Leo Pinheiro, who said the apartment was set aside for Lula and also given a costly refurbishment after his presidency in 2013.
In addition, Lula is accused of having allowed OAS to pay the storage between 2011-2016 for the many gifts he received as president.
Lula says he never owned or used the apartment.
"To prove that I'm the owner they need to have a receipt, a notary's register, a document. If I didn't pay, if I didn't have the key... then it couldn't have been mine," Lula said on SBT television.
Judge Moro is handling another case in which a second construction company, Odebrecht, is also alleged to have given Lula a bribe in the form of property.
In this case Odebrecht allegedly offered to donate 12 million reais to buy land in Sao Paulo where the Lula Institute, which seeks to preserve his legacy, was built. Prosecutors say the deal fell through and no payment was made, but the institute says nothing illegal took place.
In addition, prosecutors say that an apartment rented by Lula's wife had in fact been bought for her by Odebrecht through a third party.
In this case, Lula is accused of money laundering and influence trafficking during Brazil's $5 billion purchase, during the presidency of his Workers' Party protege Dilma Rousseff, of Swedish Gripen warplanes.
Lula allegedly received 2.25 million reais through a company run by his son Luis Claudio "to influence Dilma Rousseff in the purchase of the Gripen aircraft."
In the same case, Lula is accused of using his influence to gain tax breaks for auto makers.
This case is based on plea bargain testimony from former Workers' Party senator Delcidio do Amaral.
He accuses Lula of participating in an attempt to pay a director at corruption-riddled state oil company Petrobras not to testify in a plea bargain.
"Car Wash" prosecutors have used plea bargains with great effect to get corruption suspects to turn on each other and Nestor Cervero, the former director of Petrobras' international wing, was seen as a big fish.
Lula is accused with former BTG Pactual banker Andre Esteves, rancher and close friend Jose Carlos Bumlai, and do Amaral himself, of trying to keep him quiet.
Again, Lula is accused of influence peddling, starting in 2008 and continuing long after his presidency into 2015. In this case, he allegedly leaned on the huge national development bank, the BNDES, to favor Odebrecht when it came to projects in Angola and other countries.