Gwyrthyr ap Greidol, {Fictional, Early Welsh Texts}

This is one of the fathers of one of the Guineveres, King Arthur's wife, which comes from the Middle Welsh and Latin poetry written before Geoffrey of Monmouth; Culhwch and Owain, for instance, and the Vita Iltuti.

Culhwch and Owain is included in the Mabinogion, and can be read in English in the translation by Gwyn Jones and Thomas Jones, published in 1949.

Vita Iltuti has most recently been published by Brepols, 2011.