‘White Track’
The daughter of the chief giant Yspaddaden, and object of Culhwch’s affection in the Mabinogion story of Culhwch and Olwen. An alternate name is Niwalen. Her name appears to mean ‘White Track’, but it may also come from olwyn – ‘wheel’.
Culhwch’s stepmother swore that he should love only Olwen, and his heart swelled at the very mention of her name, even though he had never seen her. So Culhwch set out to find her, first coming to a royal court, said later to have been that of King Arthur, where the gatekeeper Glewlwyd remarked that he had never, in his long career, encountered such a handsome youth.
The King sent out messengers to look for Olwen, but a year passed without any news. Culhwch then formed a party of gifted companions to help him in his search, these companions being named as Cei (Kay), Bedwyr (Bedivere), Cynddylig the Guide, Gwrhyr, Gwalchmai fab Gwyar and Menw fab Teirgwaedd, though many others seldom named, also accompanied him.
Setting out, they at length met Custennin the Shepherd, whose wife turned out to be Culhwch’s aunt. She knew Olwen, and, even though she had lost twenty-three of her twenty-four sons to Yspaddaden, she agreed to help Culhwch, telling him that Olwen came to her house every Saturday to wash her hair. The due day came, and the couple met.
Yellower was her head than the flower of the broom, whiter was her flesh than the foam of the wave ... Whosoever beheld her would be filled with love of her. Four white trefoils sprang up behind her wherever she went; and for that reason she was called Olwen.
Olwen immediately agreed to his suit but told Culhwch that he must obtain the permission of her father. She warned him not to flinch from any conditions set or tasks imposed. Culhwch agreed, and the very next morning the party set out for Yspaddaden’s castle. For three days the giant told them to come back the next and then, when they had turned their backs, hurled a poisoned boulder at them. They were too quick and caught the boulder, which they hurled back. After three days the giant was severly weakened by his own poison, so he agreed to hear Culhwch.
He agreed that he could marry Olwen provided he carried out a number of seemingly impossible tasks. Each of these Culhwch completed, but, as Yspaddaden continued to pile condition upon condition, Culhwch rounded up all the giant’s enemies and stormed the castle. Yspaddaden was killed, and Culhwch married Olwen, the pair remaining faithful for the rest of their lives.
Olwen is also the heroine of the Mabinogion story of Culhwch and Olwen, and also of a Welsh folktale Einion and Olwen in which a shepherd, Einion, travelled to the Otherworld to marry Olwen. They had a son whom they named Taliesin.
Source
Culhwch and Olwen | Late 11th century
A Welsh Classical Dictionary | Peter Clement Bartrum, 1993