Morfydd ferch Urien is a figure of Welsh

Wales

Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...

 Arthurian legend. She is the daughter of Urien Rheged by Modron

Modron

In Welsh mythology, Modron was a daughter of Afallach, derived from the Gaulish goddess Matrona. She may have been the prototype of Morgan le Fay from Arthurian legend...

, and twin sister to Owain

Ywain

Sir Ywain is a Knight of the Round Table and the son of King Urien in Arthurian legend...

. Morfydd appears in the Welsh Triads

Welsh Triads

The Welsh Triads are a group of related texts in medieval manuscripts which preserve fragments of Welsh folklore, mythology and traditional history in groups of three. The triad is a rhetorical form whereby objects are grouped together in threes, with a heading indicating the point of likeness...

 and is also referred to in Culhwch and Olwen

Culhwch and Olwen

Culhwch and Olwen is a Welsh tale about a hero connected with Arthur and his warriors that survives in only two manuscripts: a complete version in the Red Book of Hergest, ca. 1400, and a fragmented version in the White Book of Rhydderch, ca. 1325. It is the longest of the surviving Welsh prose...

. The enduring love between her and Cynon son of Clydno

Calogrenant

Sir Calogrenant, sometimes known in English as Colgrevance, or, in ancient Welsh, Cynan ap Clydno, is a Knight of the Round Table in Arthurian legend. He is a cousin to Sir Ywain, and his courtesy and eloquence were known throughout the kingdom....

, one of Arthur's warriors, is remarked on in several of the Triads, pointing to a now lost popular tradition.

The circumstances of their birth is related in a Welsh folktale:

In Denbighshire

Denbighshire

Denbighshire is a county in north-east Wales. It is named after the historic county of Denbighshire, but has substantially different borders. Denbighshire has the distinction of being the oldest inhabited part of Wales. Pontnewydd Palaeolithic site has remains of Neanderthals from 225,000 years...

 there is a parish which is called Llanferes, and there is there Rhyd y Gyfarthfa (the Ford of Barking). In the old days the hounds of the countryside used to come together to the side of that the ford to bark, and nobody dared go to find out what was there until Urien Rheged came. And when he came to the side of the ford he saw nothing except a woman washing. And then the hounds ceased barking, and Urien seized the woman and he had his will of her; and then she said "God's blessing on the feet which brought thee here." "Why?" said he. "Because I have been fated to wash here until I should conceive a son by a Christian. And I am daughter to the King of Annwfn, and come thou here at the end of the year and then thou shalt receive that boy." And so he came and he received there a boy and a girl: that is, Owain son of Urien and Morvydd daughter of Urien.