Dafydd ap Gruffydd was a member of the royal house of Gwynedd. His father was the eldest son of Llywelyn ap Iorwerth, the ruler of Wales in the early 13th century. Born in 1238, Dafydd himself was the youngest of four sons.

His family was rocked by conflict throughout his life. With the death of his grandfather in 1240, his father and uncle fought among themselves for control of the country, resulting in Gruffydd’s imprisonment in Criccieth Castle. Dafydd’s mother pleaded to Henry III to intercede, which he did, only to imprison Gruffydd at the Tower of London, as hostage for his brother’s good behavior.

Thus, Dafydd grew up in England, as a close companion to Prince Edward, who later became Edward I of England.

Gruffydd died in 1244 when the rope by which he was trying to escape his room in the Tower of London broke and he fell to his death.

Gruffydd’s brother, who had been ruling Wales in his absence, died in 1246, leaving Wales without a primary leader. That space was filled very quickly by Llywelyn, one of Dafydd’s older brothers, the only one who had not traveled to England with his family, but had stayed at his uncle’s side throughout his father’s imprisonment.

At the time, Dafydd was only 8 years old, and in no sense prepared to put forth a claim to his patrimony. Gwynedd was thus split between Llywelyn and Owain, the eldest of the four brothers. When Dafydd came of age, Llywelyn refused to split Gwynedd further. Dafydd then appealed to Owain, and in 1255, the two conspired to gain control of all of Gwynedd for themselves. Llywelyn defeated them in the Battle of Bryn Derwin.
Initially, Llywelyn imprisoned both Dafydd and Owain at Dolbadarn Castle, but a year later, he accepted Dafydd back into his favor, even giving him lands in eastern Gwynedd centered around Denbigh. Over the next five years, Llywelyn brought Dafydd more and more into his confidence and gave him more power.

But then, suddenly in 1263, Dafydd fled Wales, switching his allegiance to Prince Edward. To this day historians have no idea why he did that, though various apologists for Dafydd have suggested that he was justifiably dissatisfied with what he was getting for his years of loyalty. Even the fact that he remained Llywelyn’s sole heir could not satisfy him.
Throughout, Llywelyn continued to gain control over greater portions of Wales. By 1267, the throne of England acknowledged his station as the principal ruler of Wales. One of the conditions of that acknowledgement, however, was that he had to once again accept Dafydd back into the fold.

Then, in 1274, Owain, son of Gruffydd ap Gwenwynwyn, the Ruler of Powys, confessed to the Bishop of Bangor, that he had conspired with Dafydd to assassinate Llywelyn, and would have succeeded but for a snowstorm.
Dafydd’s part in the plot appears to have been unknown to Llywelyn until late in 1274, when Dafydd was called to account for his actions (which he denied). It was only after Dafydd fled to England that Owain confessed to the bishop the entire plan, and Llywelyn understood fully what had been intended (Smith 1998 p. 369-373). J. Beverly Smith argues that Dafydd was the true instigator of the conspiracy (p. 376).

In 1277, Dafydd again stood at Edward’s side as he brought an overwhelming force into Wales. The victory resulted in Dafydd being awarded lands, on which he built at least three castles: at Denbigh, at Caergwrle, and at Rhuthin.
By 1282, Dafydd was again unsatisfied, but this time at his treatment at Edward’s hands. In the spring of 1282, he launched a rebellion against Edward. The war raged most of the year, but resulted by December in the assassination of Llywelyn and the fall of Wales to England.

Dafydd avoided capture for six months, but by June of 1283, English soldiers had arrested him, and in October, King Edward ordered him hanged, drawn, and quartered in Shrewsbury. Afterwards, his head was displayed for twenty years at the Tower of London alongside Llywelyn’s.