He was born about the year 880, the son of Cadell ap Rhodri and the grandson of Rhodri Mawr, the king who had held the Vikings from Wales. Inheritance, marriage and death built his realm. From his father he took Seisyllwg, the hill country of Ceredigion and the valley of the Tywi; by his marriage to Elen, daughter of the last king of Dyfed, he joined that ancient kingdom to his own and made Deheubarth, the South, ruled from the royal seat of Dinefwr; and when his cousin Idwal Foel of Gwynedd fell fighting the English in 942, the North came to him as well, and Powys with it. For eight years Hywel ruled more of Wales than any man before or since, and he ruled it by a policy his own age found strange and posterity found wise: he kept the peace with England. He travelled to the courts of Athelstan and his brothers, witnessed their charters, paid what respect was prudent, and in exchange kept his people's lands and laws untouched. In 928 he made the long pilgrimage to Rome, the first Welsh king to kneel there, and came home with the blessing of the Pope and the name of a peacemaker. The great prophetic poem of his century, the Armes Prydein, dreamed of a Britain united behind its own kings, and Hywel was the nearest fulfilment that dream ever had.

His monument is not a castle but a book. The old tradition says that Hywel summoned to Ty Gwyn ar Daf, the White House on the River Taf at Whitland, an assembly of the wisest men of Wales: the most learned in law from every commote, and with them the wisest of the clergy, and for forty days they examined the whole body of Welsh custom, law by law. What was good, they kept; what was doubtful, they amended; what was bad, they abolished; and Blegywryd, a great clerk of the church of Llandaff, wrote it down. The book they made, Cyfraith Hywel, the Law of Hywel, was ordered in three parts: the laws of the court, setting out the king's household and the rights and fees of its officers; the laws of the country, governing land and kinship, theft and surety; and the test book of the judges, the cases by which a justice proved his learning. The lawbook's own prologue adds the finishing touch of legend: that Hywel carried the finished law to Rome, and the Pope examined it and confirmed it.

What makes the law extraordinary is its temper. It is a code of compensation rather than vengeance. Killing was answered not by the rope but by galanas, the blood-price scaled to the dead man's rank, and insult by sarhaed, the honour-price, so that dignity itself had a legal value. It looks after the small with a care that still startles: a wife could leave her husband and take her share for three named causes, and one of them was bad breath, alongside leprosy and impotence. It defines the whole world of the court down to the filth-raker and the falconer, what each man may claim and what each must give. No code in Europe of that dark century is so complete, so practical, or so humane, and none lasted so long. Written in the tenth century, copied through the Middle Ages, it remained the living law of Wales until the Acts of Union of 1536 to 1543, six hundred years of a people's justice flowing from one king's forty days.

The end came quietly. In 950 the Welsh Annals record simply that Hywel, king of the Britons, died, and the unity died with him: his sons fought the sons of Idwal for the North at the battle of Carno, and Gwynedd passed back to its own line for ever. But the law did not die. Courts in every corner of Wales went on quoting the law of Hywel as the last word in justice, and the phrase became a proverb of fairness itself. The manuscripts that carry it, Latin and Welsh, are among the oldest treasures of the nation, and one silver penny, struck in his name, is the only coin of any Welsh king known to survive. Wales remembers him with a scholar's affection: the White House at Whitland keeps his centre, the health service of the west bears his name, and every retelling of his lawgiving is a quiet claim that the best of kings rule by law and not by fear. He is the proof that a crown can be lost in a generation and a law can outlive an empire, and that the man they called the Good was the one Welsh king all Wales agreed to keep.