Gwynllyg, Gwynllym, Gwynnlyw, Gynnlym, Gynnlyw
The King of Glamorgan in the Life of St. Cadoc.
He abducted Gwladys, the wife (or daughter) of King Brychan of Brecknock, and fled with her. He encountered Arthur on a hilltop. Arthur desired Gwladys, but was persuaded by Cei and Bedwyr to follow his nobler instincts and give harbor to Gwynnlyw.
Gwynnlyw and Gwladys later produced a son, Saint Cadoc.
Source
Life of St. Cadoc | Lifris, late 11th century