Dormarch survives in two golden mentions, and both are old. The first is in Culhwch and Olwen, the earliest Arthurian prose tale, composed around the year 1100. When Culhwch musters the strength of Arthur's court to win Olwen from her giant father, the roll of the summoned runs for pages and passes from kings to magicians to animals, and among them come Gwyn ap Nudd, in whom, the tale says, God set the spirit of the demons of Annwn lest this world be destroyed, and with Gwyn comes his hound, Dormarch. That is all the tale gives him: a name on the greatest list in Welsh literature. But to be named at all in that company is fame, for the roll forgets thousands and remembers the few that mattered. The second mention is older still in spirit: the dialogue poem of the Black Book of Carmarthen, where Gwyn ap Nudd, speaking with the mortal prince Gwyddno Garanhir, names his hound Dormarch in the same breath as his war-gear, as a warrior names his sword.

To know the hound, know the master. Gwyn ap Nudd, son of Nudd, is the king of Annwn, the Welsh Otherworld, the lover of Creiddylad for whose sake he fights Gwythyr every May Day until the Day of Judgment, and above all the gatherer of souls. In the old poem he tells Gwyddno that he was present where the warriors of Britain fell, that he was at Arfderydd when Gwenddolau was slain, walking the battlefields to take the dead. Where such a master hunts, his hound hunts too, and the pack that runs with Gwyn is the Cwn Annwn, the hounds of the Otherworld, the same shining white dogs with red ears that Pwyll Prince of Dyfed met at Glyn Cuch when he stumbled on the hunt of Arawn. Their colours are the colours of every Otherworld beast in Celtic story, and their cry plays tricks with distance, sounding far off when the hunt is close and close when it is far. Later Welsh folklore knew them as the pack that rides the storm, heard on wild nights over the hills, whose hearing was a warning of death, and named Dormarch, the one hound of the pack with a name, as their chief.

His name is a riddle worth keeping. In Welsh, march is a stallion, and dor is a door or gate, so the hound's name runs something like the Stallion of the Door, as if he were not a dog at all but the steed that stands at the threshold of the Otherworld, or the horse-spirit that leads the hunt through it. The doubling of horse and hound in a single name is pure Annwn, where nothing is only itself. And he is in good company, for Welsh legend loved its dogs by name. There is Drudwyn, the whelp of Greid, whose leash and collar and chain were three of the impossible tasks of Culhwch; there is Cafall, the hound of Arthur himself, whose footprint in the stone at Carn Cabal, near Builth, was counted among the wonders of Britain in the ninth century, a print that returns to the cairn however often the stone is taken away. Ireland went further and named its greatest hero for a dog: Cu Chulainn, the Hound of Culann. Dormarch belongs to that ancient honour-roll of Celtic hounds, and outranks them all in one respect, for he alone runs with the dead.

The Wild Hunt he leads has never slept. As Gwyn ap Nudd's pack it rode out over Wales on the nights of winter, and under other names it rides all over Europe: the Gabriel Hounds of the north of England, the Devil's Dandy Dogs of Cornwall, the hunts of Odin and of Herne. But the Welsh tradition keeps the gentlest touch of any of them, because it keeps the dog. Somewhere in the storm there is still a white hound with red ears at the front of the cry, a stallion's name on a hound's lean shoulders, running point for the king of Annwn as he gathers what the battlefields leave. The oldest Arthurian tale remembered to summon him, and a thousand years later his name still answers.