Mr O'Brien believes it is part of a conspiracy to damage his reputation
A Dublin PR firm insists a dossier on businessman Denis O'Brien was compiled on behalf of a confidential client, and not because of any grudge.
Mr O'Brien is looking for a court order to reveal this person's identity because he believes it is part of a conspiracy to damage his reputation.
In October, Mr O'Brien anonymously received a USB stick which contained hundreds of files about him.
He claims it confirmed his suspicions that a conspiracy was underway to blacken his name and hurt him commercially.
He hired a private investigator and a team of computer experts who led him to the door of Red Flag Consulting Limited.
The Dublin PR firm admits putting the dossier together but said it was not because of any grudge against the businessman - and was done on behalf of a client.
Counsel for Mr O'Brien is now looking for a court order to reveal the identity of this mystery client.
Most of the files are newspaper cuttings, but the court has been made aware of three documents allegedly defaming him.
One of them describes him as 'Ireland's Berlusconi' - while another describes his charitable acts in Haiti as 'self-serving' and a means to 'throw off the negative shroud of the Moriarty Tribunal'.
Red Flag denies any wrongdoing.