To date, little is known about the publicity-shy solicitor, who has preferred to remain in the background in relation to his extensive involvement in a number of property dealings under scrutiny by the tribunal.
Mr Caldwell's name first came to prominence last year when he failed to respond to a summons issued by the tribunal to attend a public hearing of the inquiry as a witness.
The solicitor had attracted the attention of the tribunal over his role as legal adviser to property developers, Tom Brennan and Joe McGowan. Tribunal chairman, Mr Justice Feargus Flood, recently ruled that the pair had made a series of corrupt payments of over £125,000 to former Fianna Fáil minister, Ray Burke.
Much to the annoyance of Mr Justice Flood, a summons sent to Mr Caldwell's home in Dublin was returned to the inquiry's offices in Dublin Castle unopened. Indeed, the tribunal chairman warned the solicitor would face prosecution unless he appeared to give evidence.
"It is a very serious matter when any citizen openly defies a tribunal of inquiry established pursuant to a resolution of the Oireachtas. It is profoundly disquieting when such defiance comes from a solicitor," remarked Mr Justice Flood He appeared to take particular offence at Mr Caldwell's explanation that his non-attendance was a result of the fact he had ceased practising as a solicitor a few weeks earlier and was no longer an Irish citizen or resident.
Mr Caldwell also informed the tribunal he had moved outside the State and no longer held a certificate to practise as a solicitor in the Republic. Such claims, however, didn't wash with the tribunal, with Mr Justice Flood dismissing such assertions as "spurious".
It was only after the tribunal referred the matter to the High Court that Mr Caldwell finally relented and showed up in Dublin Castle to explain his involvement in the transfer of Brennan and McGowan's funds to Ray Burke.
With no sense of incongruity, he declared that his "level of recollection" on that occasion was quite different to when he was first contact by the tribunal.
For his troubles, Mr Justice Flood ruled in his interim report that the solicitor had failed to co-operate with the tribunal on three separate counts a matter over which Mr Caldwell could still face a massive legal bill and criminal prosecution.
However, worse days may lie ahead for the balding, bespectacled solicitor as he played a more central role in matters which the tribunal has just begun to investigate.
As one tribunal lawyer remarked last year, Mr Caldwell has had "a pervasive presence" a thinly-veiled reference to the fact that the solicitor's name has sprung up in several separate avenues of the inquiry's exhaustive examination of planning in Dublin during the late 1980s and early 1990s.
Mr Caldwell's lawyers admitted for the first time this week he is one of the ultimate, beneficial owners of the secretive, English-registered company, Jackson Way Properties. The acknowledgement provided further proof the tribunal has finally won a long, hard-fought battle to discover the true owners of the company. In turn, Jackson Way is closely linked to another company, Paisley Park Investments, which paid £25,000 to politicians via Frank Dunlop in return for votes on a controversial rezoning at Carrickmines in south Dublin in the early 1990s.
Only a few weeks ago, a Birmingham estate agent, Alan Holland, had sworn on oath that he was the sole owner of Jackson Way at an arbitration hearing in which the company is seeking 47m from Dun Laoghaire-Rathdown County Council.
Mr Caldwell has also had his name linked with other high-profile individuals under investigation by the tribunal, including Liam Lawlor and businessman, Jim Kennedy, as well as another controversial planning development at Portrane in north Co Dublin.
The solicitor's association with such individuals lends support to his own recent description of himself as a "businessman".
However, it is widely believed that he first came into contact with Mr Lawlor and Mr Kennedy through his work as a solicitor, in particular because of his expertise in the complex area of taxation and company law.
Belfast-born Mr Caldwell, who is believed to hold dual citizenship, qualified as a solicitor in 1980 and spent many years until recently working as a senior partner with the Dublin firm, Binchy's.
Although it's no surprise to discover that a member of the legal profession enjoys considerable wealth, Mr Caldwell certainly has attained a level of affluence not normally associated with a solicitor with such a low public profile.
He currently resides in a luxurious, secluded mansion called Belfort on Strathmore Road, Killiney, Co Dublin, with his wife, Ena. The house, with its extensive gardens, fits easily into the depiction of the area as Millionaire's Row and is just a stone's throw away from neighbours like U2 singer Bono and the residence of the Canadian Ambassador.
Whatever else about his knowledge of Dublin property, Mr Caldwell knows a good postal address when he sees one.