Dyrnwch
An Irish giant. He was steward of Odgar of Ireland. Diwrnach owned a magic cauldron, which would only boil if the meat placed in it was intended for a brave man. It was listed in Welsh lore among the Thirteen Treasures of the Island of Britain.
As one of his tasks, Culhwch had to obtain this cauldron from Diwrnach for boiling meat at Olwen’s wedding feast. When Arthur, on the behalf of Culhwch led an expedition to Ireland, requested the cauldron, Diwrnach refused. At this refusal, Arthur’s warrior Llenlleawg (Llenllawc Wyddel) killed Diwrnach and took the cauldron, which Arthur’s warriors filled with Ireland’s treasure before returning to Britain.
The appearance of a wondrous Irish cauldron in this tale leads to a possible identification between Diwrnach and the Daghdha and later with the Holy Grail.
Source
Culhwch and Olwen | Late 11th century
Triads of the Island of Britain (Welsh ”Triads”) | 11th century to 14th century