The Commercial Court has agreed to fast-track separate cases against former Irish Nationwide boss Michael Fingleton and four former directors.
Mr Fingleton and others are being sued for tens of millions of euro over the management of the building society in the years before it was nationalised, when it ran up losses of more than €6bn.
Mr Fingleton is being sued for breach of contract, gross negligence and breach of duty as a director and chief executive.
It is claimed his actions caused the "extraordinary losses" suffered by the building society.
An attempt will also be made to recover a €1m bonus paid to him shortly before he left the society in 2009.
IBRC claims Mr Fingleton would have been fired if the true picture of how the society was run was known at the time.
It is also claimed he received expenses which should not have been paid to him.
In separate proceedings, former directors Terence Cooney, Stan Purcell, David Brophy and former chairman Michael Walsh are being sued for tens of millions of euro for alleged breach of duty in allowing Mr Fingleton to have too much control.
Sworn statements submitted to court claim there was an "unusual management structure", where the board of INBS delegated by resolution all of its powers to Mr Fingleton, giving him significant responsibility and autonomy on lending and decision making.
There was an excessive concentration of powers in his hands, the statement said.
The court was told INBS suffered losses of more than €6bn arising from the impairment of its loan book.
A considerable part of the "catastrophic losses" were from loans for commercial property up to September 2008. It was later nationalised and its assets transferred to IBRC, formerly Anglo Irish Bank.
Mr Fingleton ran the society from 1971 to 2009. However he left "astonishingly little" behind him by way of written record of his actions.
Therefore transactions had to be "reconstructed” to ascertain the true position of what was going on in INBS.
The case against Mr Fingleton centres on the manner in which INBS was managed prior to the State guarantee, both generally and with regard to specific transactions.
Counsel for the bank Maurice Collins said hundreds of transactions had been looked at a 20 transactions had been subjected to detailed forensic review.
The case relates to the lending policies in place since 2002, the adequacy of those policies and if they were implemented and the corporate governance structure.
He said it was in the public interest to have the case heard in the fast-track Commercial Court.
It was "a significant claim involving a significant investigation into a significant financial institution over a number of years" he said.
Mr Justice Peter Kelly said Irish Nationwide's assets were transferred to NAMA in two tranches with discounts of 50 and 75%, the largest discounts of all financial institutions engaged in the NAMA process.
The case against former directors Terence Cooney Stan Purcell, David Brophy and former chairman Michael Walsh was also accepted into the Commercial Court list.
IBRC claims they improperly delegated enormous power to Michael Fingleton in breach of their obligations to the building society.
Mr Justice Kelly adjourned that case for five weeks to allow time to agree a timetable for exchange of documents. He noted the four were in a very different position to Mr Fingleton with regard to their state of knowledge.
Some intend to seek security for costs against IBRC to ensure the bank, which is now in special liquidation, could meet the costs of the action should it lose the case.
Mr Justice Kelly did not accept there had been undue delay in bringing the actions as there was a "huge exercise" undertaken in order to get to grips with what was going on at the building society.
He said the statement of claim lodged by the plaintiff at 80 pages was one of the most detailed he had ever come across.
The case against Mr Fingleton is unlikely to be heard before early next year.
Details of expense claims emerge
Court documents in the case against Mr Fingleton show large sums were paid out in expenses for travel, hotels, healthcare and gifts.
Irish Nationwide paid €90,000 for pension advice and arrangements for the former CEO.
Tens of thousands of euro were also paid for meals and accommodation in top restaurants and hotels both in Ireland and abroad.
In documents submitted to the commercial court, IBRC claims expenses were claimed for flights, private chauffeur services, golf, jewellery and entertainment.
IBRC claims some of the expenses were not appropriately incurred in connection with the business of the society.
According to court documents which detail expenses claims for Mr Fingleton from 2002, the society paid for entertainment and presents provided to some well-known business people, including €3,255 claimed for a present for Michael Smurfit from a liquor store in St Bartlelemy in the Caribbean and a €1,000 Brown Thomas gift token for a daughter of developer Gerry Gannon.
It paid €6,000 for a Gucci watch bought at auction in 2006 by Mr Fingleton and later re-auctioned with the funds given to the charity, the Jack & Jill Foundation.
€4,525 was also claimed for a New York jeweller, Maurice Columbus and €8,000 for a Caribbean jeweller.
Various sums were claimed for hotels and restaurants in New York, Beverley Hills, Dubai, London, Marbella, Monaco, Moscow, St Petersburg, Scotland, Dublin and Wicklow, including the Waldron Astoria and 21 Club in New York and Patrick Guilbaud's in Dublin.
€4,000 was claimed for entertainment for developers Sean Mulryan and Louis Scully, solicitor Paul Wallace and others at Annabel's Private Club, Berkeley Square, London, while €7,000 was paid for a two-night stay in Dublin's Westbury Hotel in February 2009 for Mr Fingleton and others described in the documents as "O'Hare, Parker, Empson, Dawson and McCollum".
€2,373 was claimed for a three-night stay in London's Dorchester Hotel in May 2009 for Mr Fingleton and his wife, plus €12,180 for dental fees over two months in 2008.
Other expenses were €2,086 to Trailfinders for a six-night trip to Dubai in 2005 and €1,000 for a 2005 trip with Michael Smurfit, Sean Mulryan and Arthur French.
Mr Fingleton also claimed expenses for membership of the K Club, trips with Private Chauffeurs Ireland, rounds of golf, other medical treatment, food and drink levies and for sums in cash.