Hueil belongs to the large family of Caw in the Welsh tradition. Culhwch and Olwen includes him in its roll call of Arthur's companions, alongside several brothers, while giving him an unusually independent reputation. The same tale says that Hueil stabbed his nephew Gwydre son of Llwydeu and that this wound caused hostility between Hueil and Arthur. This Gwydre should not be confused with Arthur's son of the same name. The brief notice does not explain the entire quarrel, but it makes clear that inclusion in the court list need not mean an uncomplicated history of loyalty.

The Life of Gildas develops the quarrel into a sustained challenge to Arthur's authority. Hueil is presented as an outstanding warrior who will not submit. He repeatedly descends from Scotland, burns settlements and carries off plunder, while some people hope that he will become king. Arthur pursues him and kills him on the island called Minau, commonly identified with the Isle of Man. The account is a medieval saint's life, not a contemporary record of a sixth-century campaign; its account of the brothers and their opposition belongs to that literary setting.

Gildas hears of his brother's death while he is in Ireland. His grief does not prevent him from praying for Arthur as well as for Hueil. When he returns to Britain, clergy and other people bring about a reconciliation, and Arthur accepts the penance imposed by the bishops. A different tradition reported by Gerald of Wales says that Gildas destroyed books praising Arthur after his brother was killed. This is a story about lost writings, not evidence that those particular books have been recovered or that their contents can be reconstructed.

Elis Gruffudd's later account moves the conflict to Ruthin and gives it a personal cause. Hueil and Arthur quarrel over a woman, and Hueil wounds the king's knee. Their settlement requires him never to mention the injury. When Arthur later dances in disguise among women, Hueil recognises the affected knee and makes a mocking remark. Arthur treats the remark as a breach of the promise and has him beheaded. The episode must remain separate from the killing on Minau: its different setting and cause show how the same rivalry could be retold.

The Welsh Triads and proverbial verse preserve further traces of Hueil's reputation without providing a complete biography. At Ruthin, Maen Huail gives the later execution story a material focus. Cadw records a limestone stone of uncertain original date and purpose, possibly a civic, market or preaching stone, with an inscription referring to the beheading tradition. The object is real, but its survival does not authenticate the execution. Hueil's significance lies in the tension between an independent warrior, an expanding royal authority and the different ways storytellers explained their fatal encounter.