Separating the man from the myth is a difficult task, as more stories survive about his youthful adventures, than factual records of elements of his real life. However, his life was documented by playwrights and biographers alike, so we do have access to a few facts. Twm Sion Cati's real name was Thomas Jones, who was actually a Welsh bard and genealogist. He lived from 1530 to around 1620, and was born at a house called Porth y Ffynnon (Fountain Gate) in Tregaron.

Whilst the story insists that Jones was the illegitimate son of a local squire - Sir John Wynn of Gwydir, his father was actually John, son of David ap Madog ap Howel Motheu. His mother was Catherine, daughter of Meredydd ap Ieuen, which is where the 'Cati' part of his name came from.

In his early years, Jones developed a reputation as Twm Sion Cati, the highwayman, supposedly only robbing the rich, although there is little evidence of him regularly giving to the poor. In 1833, Samuel Lewis wrote, in his book 'A Topographical Dictionary of Wales' 1833 that, "he enjoyed, according to tradition, a less enviable distinction, from his practice of plundering his neighbours, being represented, as an expert and dexterous robber".

It is known that Jones received some formal education, and was reputed as being clever and crafty; a trickster who was capable of deceiving farmers and lords alike. In most of the stories about Twm, he is perhaps best remembered for his kindness to his victims. Wishing to avoid severely hurting or killing them, he avoided maiming his enemy by placing a well shot arrow that pinned his nemesis to his saddle.

One famous story tells of Twm's visit to an ironmonger's in Llandovery to buy a porridge pot. The ironmonger brought out several pans and Twm on questioning the quality and costs of the pans was told that no better would be found in the kitchen of a king. Twm then held one of the pots up to the light and declared that he could see a hole in it. The ironmonger then held up the pot to examine it and Twm forced over his head and quipped that if there was not a hole in it how could such a large and stupid head have been caught inside!

Often he hid from the Sheriff of Carmarthen in the slopes of the thickly wooded and boulder strewn slopes of the Dinas Hill, close to the village of Rhandirmwyn, Carmarthenshire. The village is located in the foothills of the Cambrian Mountains, whose rough and rocky terrain made ideal bandit country.

Twm's hideout is widely known as a cave that resides in the slopes directly above a rocky gorge through which the Tywi flows at an extremely dangerous pace. To this day the cave is still quite difficult to locate, and bears the name, 'Twm Sion Cati's Cave'. Dinas Hill is now an RSPB sanctuary, a way-marked footpath runs right around the hill, with a detour to Twm's cave.