Caw was born in the Old North, in the land the Welsh called Prydyn and later generations called Pictland, a realm of misted mountains and tribal kingdoms that lay beyond the crumbling Roman frontier. His seat was in the region of Alt Clut, the kingdom of the Rock that would later be known as Strathclyde, near the peaks of Mount Bannauc in the Cathkin Hills south-east of modern Glasgow. The 11th-century Life of Saint Cadog places his dwelling near this horn-shaped ridge, and the landscape of those hills - steep, wooded, and haunted by the remnants of older peoples - shaped the man who would become one of Arthur's most trusted northern allies. In the Life of Saint Caradog, Caw is described as a giant and regarded as a saint, a dual nature that reflects the borderland between pagan heroism and the Christian tradition of making saints in which he lived. He was a craftsman as well as a warlord, a man whose skill with his hands earned him the wealth and standing to raise a vast family in an age when most chieftains counted their followers in dozens rather than scores.

The defining episode of Caw's life belongs to the tale of Culhwch and Olwen, the oldest surviving Arthurian romance, written down in the late 11th century but preserving traditions far older. Culhwch, a cousin of King Arthur, fell in love with Olwen, the daughter of Ysbaddaden Chief Giant, a creature so vast that his eyelids had to be propped up with forks. Ysbaddaden set Culhwch forty impossible tasks, or anoethau - a Welsh word for trials that no mortal should face - as the price for his daughter's hand. Among them was the procurement of a tusk from Ysgithyrwyn Chief Boar, a beast whose white tusk was the only implement sharp enough to shave the giant's beard. But Ysbaddaden declared that he would accept the tusk from no man except Caw of Pictland. Culhwch therefore had to travel to the northern wilderness and convince Caw to leave his kingdom, cross the breadth of Britain, and serve as the giant's barber.

The hunt for Ysgithyrwyn was one of the most terrible undertakings in all Arthurian legend. Arthur himself led the chase, accompanied by his warriors, his hounds, and Caw mounted upon Arthur's own mare Llamrei. The boar was a monster of the ancient woods, a creature that had eluded every hunter who pursued it. When the beast was finally cornered, it was not the hounds that Ysbaddaden had named that brought it down, nor Odgar son of Aedd the king of Ireland who had been prophesied as the only man who could draw the tusk from the living boar. Instead, Caw of Pictland rode forward on Llamrei, raised a hatchet, and split the boar's head in two halves with a single terrible blow. He claimed the tusk and carried it to Ysbaddaden's fortress, where he personally shaved the giant's hair, flesh, and skin down to the bone, and both ears completely, fulfilling the task that no other man could perform. The violence of that shaving - the razor of a boar's tusk peeling a giant's face - is one of the most visceral images in Welsh storytelling, and Caw stands at its centre.

Caw's service to Arthur extended beyond the boar hunt. When Arthur sought the blood of the Very Black Witch, daughter of the Very White Witch, from the Head of the Valley of Grief in the Uplands of Hell, Caw accompanied the expedition. Arthur killed the hag with Carnwennan his little knife, striking her until she was as two tubs, and Caw collected her blood and kept it with him. These two acts - the shaving of the giant and the collecting of the witch's blood - mark Caw as Arthur's man of grim necessities, the warrior who did not flinch from the monstrous tasks that other knights found beneath their honour. He brought his entire brood to Arthur's court, a host in themselves, and the court list in Culhwch and Olwen names them all: Angawdd, Ardwyad, Calcas, Celyn, Coch, Conyn, Cynwal, Cywyllog, Dirmyg, Edmyg, Ergyryad, Gildas, Gofan, Gwarthegydd, Gwenabwy, Gwyngad, Hueil, Llwybyr, Iustig, Mabsant, Meilyg, and Neb. Among them, Gildas would become the most famous, the monk who wrote De Excidio et Conquestu Britanniae, the furious sermon that condemned Britain's kings for their sins. Hueil, the eldest, would become Arthur's rival, a warrior so proud that he never submitted to a lord's hand, who led raids from Scotland into Arthur's territory and was eventually pursued and killed by the king himself on the Isle of Man.

The Welsh Triads remember Caw as the father of a line of Pictish saints, a tradition that connects the warlord of the north to the Christianisation of Britain. The Triads, those mnemonic catalogues of Welsh heroic lore compiled in the 13th century but drawing on far older material, name him in Triads 21, 81, and 96 as the progenitor of holy men. This saintly lineage sits uneasily beside the figure who swings a hatchet at a boar's skull and shaves a giant to the bone, but it reflects the complex reality of the Arthurian Age, in which the same northern warlords who raided Romano-British towns also sheltered the monks who preserved learning through the dark centuries. Caw's daughter Gwenabwy married Llwydeu son of Nwython and bore Gwydre, a figure who may be identical with Arthur's own son of the same name, suggesting a web of kinship between the Pictish house and the royal line of Camelot that the later French romances would forget but the Welsh tradition never did. In the end, Caw of Pictland stands as the bridge between the historical Picts of the Old North and the mythic world of Arthur, a craftsman-warlord whose sons carried his name into every corner of British legend.