Griffith
The King of Wales after Caradoc, his brother. As Caradoc grew old and infirm, he gradually relinquished more power to his brother, but Griffin coveted the entire throne. Eventually Griffin had Caradoc murdered during a hunt. The noblemen of Wales were suspicious, but Griffin kept them silenced through fear.
He tried to murder Caradoc’s children, Meriadoc and Orwen, but they were saved by Ivor, their foster-father, and taken into hiding. Meriadoc eventually arrived at Arthur’s court and, after winning favor, convinced Arthur to summon Griffin for trial.
Griffin refused and fortified himself in Snowdon, but a domestic revolt combined with Arthur’s siege led him to surrender. He was properly tried and executed, and his kingdom was given to Meriadoc.
Source
Historia Meriadoci Regis Cambrie | Late 13th century