Rhodri ap Merfyn ( 820–878), later known as Rhodri the Great , succeeded his father, Merfyn Frych, as King of Gwynedd in 844. Rhodri annexed Powys c. 856 and Seisyllwg c. 871. He is called "King of the Britons" by the Annals of Ulster. In some later histories, he is referred to as "King of Wales", although the title is anachronistic and his realm did not include southern Wales.