Drudwyn was born as the whelp of Greid son of Eri, a figure who appears in the court list of Culhwch and Olwen as one of Arthur's own warriors and who was later taken prisoner by Gwyn ap Nudd, the king of the Welsh Otherworld. The name Drudwyn means something close to "fierce" or "strong" in the Brittonic tongue, and the hound lived up to it from the first. He was not a pet or a lapdog; he was a war-hound, bred for the chase of monsters, and his reputation was such that Ysbaddaden Chief Giant, when setting Culhwch his forty impossible tasks, named Drudwyn specifically as the only hound who could hunt Twrch Trwyth. The giant did not stop there. He added that Drudwyn could not be held with ordinary gear, and he listed the three pieces of equipment that would be needed: a leash made by Cors Hundred Claws, a collar made by Canhastyr Hundred Hands, and a chain made by Cilydd Hundred Holds. These were not mere craftsmen; their names suggest beings of supernatural dexterity, and the making of Drudwyn's harness was itself one of the lesser anoethau, the impossible tasks that littered Culhwch's path to Olwen.

The hunt for Twrch Trwyth was the greatest chase in Arthurian legend, and Drudwyn was at its centre. Twrch Trwyth was no ordinary boar. He was an Irish king named Taredd who had been transformed by God into a swine as punishment for his sins, and he carried between his ears a comb, a pair of scissors, and a razor that Ysbaddaden needed to shave his own beard. The boar had venom-dripping bristles, seven piglets who fought beside him as warriors, and a cunning that matched his strength. When Arthur and his host tracked him to Ireland, Twrch Trwyth defeated them and laid waste to a fifth of the island before swimming across the Irish Sea to Wales. The pursuit ranged across Pembrokeshire, Carmarthenshire, the Amman valley, and the Brecon Beacons, with Arthur losing men at every turn. Drudwyn, along with the two whelps of the bitch Rhymhi and the hounds Aned and Aethlem, formed the pack that finally cornered the beast.

The defining moment of Drudwyn's career came at the mouth of the Severn, where Arthur mustered his troops to halt the boar before it could reach Cornwall. The fight was desperate. Twrch Trwyth waded into the river, and Arthur's men managed to wrest the razor and scissors from between his ears while he was in the water, but the comb remained stuck fast. When the boar touched the riverbed with his feet, he bolted with such speed that no hound could hold him, and the chase continued across England and down into Cornwall. There, at the very edge of the land, Arthur and his warriors made their final stand. The comb was finally taken, and Twrch Trwyth was driven off the cliffs into the sea. The text of Culhwch and Olwen ends the episode with a haunting line: from then on it was not known where he and Aned and Aethlem went. Drudwyn's fate is not recorded separately, but the implication is that the greatest hunt in Welsh legend ended with the hounds still in pursuit, the boar vanished beneath the waves, and the quest fulfilled.

Drudwyn's service to Arthur extended beyond the hunt for Twrch Trwyth. The same hound was also used in the hunt for Ysgithyrwyn Chief Boar, the white-tusked monster whose tusk became the razor that shaved Ysbaddaden's face. In that hunt, Drudwyn was paired with Arthur's own hound Cafall and the pack that Caw of Picland brought from the north, a host of hounds so numerous that the forest shook with their baying. The two boar hunts - Ysgithyrwyn and Twrch Trwyth - are the twin pillars of the animal-chase tradition in Culhwch and Olwen, and Drudwyn is the only hound named in both. His owner, Greid son of Eri, was one of the three most unfortunate prisoners in the tale, held captive by Gwyn ap Nudd in the Otherworld, which suggests that Drudwyn's origins were as otherworldly as the beasts he was bred to hunt.

The legacy of Drudwyn is the legacy of the Celtic hunting hound itself, the ancestor of every greyhound and wolfhound that ever ran across the British Isles. In Welsh tradition, the hunting dog was not merely a tool but a companion of heroes, a creature that stood between the human world and the wilderness of monsters. Drudwyn, with his special leash and collar and chain, with his need for Mabon the huntsman, and with his role in the greatest chase ever told, embodies that tradition at its most extreme. He is not a pet; he is a weapon, a tracker, and a force of nature, and without him the comb of Twrch Trwyth would never have been taken, the beard of Ysbaddaden would never have been shaved, and Culhwch would never have won Olwen. In the end, the oldest Arthurian tale is as much the story of a hound as it is the story of a king.