Who is Davydd ap Gruffydd from The Reckoning and what is their importance?

Davydd ap Gruffydd is a younger brother of Llewelyn ap Gruffydd. He fights alongside his brother Owain in rebellion against Llewelyn. Owain is imprisoned, but Davydd is forgiven. Davydd rebels a second time and is exiled to England. He is again forgiven after a few years and returns to Llewelyn's court. Without a son, Llewelyn makes Davydd his heir, but Davydd is still not satisfied. Davydd plots to kill Llewelyn, but immediately regrets the plot. When the murder is thwarted because of a mudslide, Davydd gives up his plans to overthrow Llewelyn. Llewelyn discovers the murder plans and confronts Davydd, but Davydd has a cunning wit and quick tongue. He is able to temporarily convince Llewelyn that he has been unfairly accused. He flees to the court of King Edward where he is welcomed as an enemy of Llewelyn.