Cadell ap Rhodri (854~909) was the son of Rhodri Mawr ("the Great"). He inherited the kingdom of Seisyllwg from his father in 878, and passed it to his son, Hywel Dda ("the Good"), on his death in 909. Cadell and Hywel had previously conquered Dyfed in 904/905, establishing Hywel as the king in that region. After his father's death, Hywel merged the two kingdoms to establish Deheubarth.