No public IJR answers mention Gruffydd Maelor I yet. As people ask about it and share their answers, they'll appear here.
Overview
Gruffydd Maelor was a Prince of Powys Fadog in Wales. He married a daughter of King Owain Gwynedd, first Prince of Wales, and was a brother of Prince Owain Brogyntyn, ancestor of the Barons of Cymmer-yn-Edeirnion.