:: What is Nama and Project Eagle?
Nama, or the National Asset Management Agency, is the Republic's state assets agency created in 2009 in the wake of the financial crash.
Sometimes referred to as a 'bad bank', it acquired billions of euro worth of property loans from struggling Irish banks in a bid to restart the economy.
The vast portfolio included property loans in Northern Ireland, which it was decided would be sold off in one deal, known as Project Eagle.
The northern portfolio was sold to US investment fund Cerberus in 2014 for more than £1bn.
:: How did Project Eagle become controversial?
In 2015, TD Mick Wallace alleged in the Dáil that £7m linked to the sale was placed in an offshore bank account and was "reportedly earmarked for a Northern Ireland politician or political party".
The explosive allegation led to parliamentary probes on both sides of the border and an investigation by the UK's National Crime Agency (NCA).
:: Who are Frank Cushnahan and Ian Coulter?
Frank Cushnahan (78), who lives in Holywood, Co Down, is a prominent businessman and a former member of Nama's Northern Ireland advisory committee.
He has had various roles including chairman of the Belfast Harbour commissioners and maintenance firm Red Sky.
In 2011 he became the first Catholic to address the Presbyterian General Assembly.
Ian Coulter (49) is a solicitor who was formerly managing partner of Belfast-based law firm Tughans, which had indirectly acted on behalf of Cerberus.
He had joined the practice from a City of London firm in 1997 and had been a partner in Tughans since 2001 before becoming its managing partner.
Mr Coulter is also a former head of the Confederation of British Industry in Northern Ireland.
:: Why has the investigation taken so long?
It has taken more than five years to get to this point where two people, Mr Cushnahan and Mr Coulter, are facing fraud charges in relation to Project Eagle.
The NCA took the lead on investigating the Nama deal in 2015, and in 2018 a file on some initial matters was sent to the Public Prosecution Service (PPS).
The NCA interviewed 66 witnesses and identified nine suspects in its long-running probe.
Its deputy director of investigations Craig Naylor said it "has been and remains an incredibly complex investigation".
Ciaran McQuillan, PPS assistant director, described the probe as "wide-ranging" with a "considerable volume" of evidence submitted.