Real World Background
The story of Gawain and Ragnal (whose name is also spelled Ragnall, Ragnell and Ragnelle) comes from a 15th century poem, The Wedding of Sir Gawain and Dame Ragnelle, and a later ballad, The Marriage of Sir Gawain, which is a retelling of the same story. (Other variants exist, such as the Wife of Bath's Tale in Chaucer's Canterbury Tales, though it leaves the knight and lady anonymous and changes many of the details.)
This story tells of how King Arthur Pendragon fell into the power of a knight named Sir Gromer Somer Joure, who overcame the king but agreed to spare his life if Arthur would return to him a year later and answer the question: what do women most desire? Arthur spent the next year asking everyone he met this question and receiving many answers - none of which satisfied him. At the end of the year, as he made his way back to Gromer's castle, he met a hideous old woman who told him that she knew the correct answer, but would only reveal it to him if one of his knights agreed to wed her. Desperate, Arthur agreed to her terms and learned the answer: "Women most desire their own way." He gave the answer to Gromer, who reluctantly admitted it to be the truth and let him go.
But Arthur now had to fulfill his agreement to the hideous old woman. Most of the knights of the Round Table refused to marry her, but Gawain agreed to accept her. After the wedding ceremony, they retired to Gawain's quarters, where the old woman changed into a beautiful young woman, revealing that she had been under a curse that Gawain had partly broken by marrying her. However, half the curse was still in operation; she would still have to resume her hideous form for half the day. She asked Gawain whether he would rather have her be beautiful by day and ugly by night, or ugly by day and beautiful by night, pointing out the advantages and disadvantages of both choices. Gawain decided to give her the choice - and by so doing, freed her from the remainder of the spell, so that she would be beautiful by both day and night.
In Roger Lancelyn Green's retelling of the Arthurian legend, Ragnal disappeared seven years after her marriage to Gawain, with the hint that she retreated into a forest somewhere in Wales where she gave birth to a son; Green suggests that this son was Percival, inspired by the legend of the "Fair Unknown", a son of Gawain's who, like Percival, is raised in a remote forest in secrecy, but comes to Arthur's court as a young man and is knighted. This was the inspiration of Greg Weisman's take on Percival's parents. 
Although Ragnal has not been directly mentioned in Gargoyles as yet, the Spirit of Destiny addressed Peredur as "Peredur fab Ragnal", Welsh for "Peredur son of Ragnal", making Ragnal a step closer to canonicity than most other canon-in-training characters.