MP and playwright Richard Brinsley Sheridan wrote that "the usage of Roger O'Connor, who is one of the finest fellows I ever saw, has been merciless beyond example".

Following these troubles, O'Connor moved to Dangan Castle, Summerhill, County Meath having acquired the property on a permanently renewable lease from Thomas Burrowes of the East India Company.

Many years later his son Francis (then known as Francisco) wrote in his autobiography that he had accidentally started the fire himself when melting lead to make bullets.

[2][8] In 1817 O'Connor and his son Arthur were arrested on a charge of having organised a mail robbery five years earlier, during which a guard was shot and killed.

[9]O'Connor's later attempt to sue one of the accusers for perjury brought out details of events on the night of the robbery that led to continued suspicion against him.

While in Paris, O'Connor prepared his best-known work, the Chronicles of Eri (1822), a book purporting to be a translation of ancient manuscripts detailing the early history of the Irish people.

The book was prefaced by a portrait of O'Connor holding a crown, the caption to which proclaimed that he was the "Head of his Race" and "Chief of the prostrated people of his nation", a position he claimed as the supposed lineal descendant of the 12th-century king Ruaidrí Ua Conchobair.

[7] The book gives a history of the Gaels from supposed records written by "Eolus", who is said to have lived fifty years after Moses.

It claims a continuous existence of the Gaelic people, originating among the ancient Phoenicians, migrating to Scythia, Spain and then Ireland.

William John Fitzpatrick in the Dictionary of National Biography stated that the book is "mainly, if not entirely, the fruit of O'Connor's imagination".

He lived for the rest of his life in a fisherman's cottage in Ballincollig, cohabiting with a local young woman he called the "princess of Kerry".

[1] According to Richard Robert Madden, O'Connor genuinely believed that this "young girl of humble origin" was really a princess: "The enthusiasm with which he is said to have been wont to speak of the exalted claims of this princess of Kerry to an ancient Irish regal origin, left no doubt on the minds of many who heard him expatiate on this subject, that he had worked himself up into a firm belief in his fondly-imagined discovery.

Prendergast concludes that O'Connor showed great courage in his patriotic statements during his arrest and imprisonment for alleged sedition, but that his eccentric personality and Irish nationalism "rendered him so odious [in the eyes of his enemies] that the grossest charges would be willingly believed".

[7] James Dunkerley says that several authors have described O'Connor as "a little mad", adding that the Chronicles of Eri is a "colourful concoction - a more 'imagined community' it would be hard to locate outside of Atlantis".

[1] Madden considered him to be possessed of considerable "cleverness, cunning, astuteness and plausibility", but argued that the personal charm and persuasiveness that made his conversation and speech-making so powerful, was never translated into print.

His writings were bombastic: "he wrote in the genuine Boanerges Bombastes-Furioso style, wherein the swaggering Pistol talked in the true Ercles vein.