Howell was through his father, a descendant of Rhodri Mawr and thus a member of the Dinefwr branch of the dynasty originating from Powys. It is known as the most successful Welsh rulers from the period before the Norman Conquest. His name is associated with the development of the Welsh laws, also known as the Laws of Hywel ( Hywels laws ) are known. They have been handed in Llyfr Gwyn Hergest ( "The White Book of Hergest ").
Howell the Good was around 880, born a younger son Cadell ap Rhodris, a son Rhodri Mawrs. After Cadell Dyfed had conquered, he gave it to his son, who was to govern it in his behalf. Hywel was able to consolidate its position as rulers nor by marrying Elen, whose father was himself ruler of Dyfed before his death. After his father was 909 died, he inherited a portion of Seisyllwg and united after the death of his brother in 920 Dyfed and Seisyllwg. So he created a new kingdom, which became known as Deheubarth. After the death of his cousin Idwal Foel in 942 he also took control of Gwynedd and ruled more than three-quarters of today's Wales '. Hywels regency was not characteristic of that time, for he hardly led wars and reached a friendship relationship with Æthelstan of England. The relationship between the two countries enabled that Hywel was minting in the English city of Chester the first and only Welsh ruler who has ever had its own currency, its own coins. The study of the English legal system and the pilgrimage to Rome in 928 - of course he wanted to have the option of one of the Popes John X, Leo VI. or Stephen VII, who sat this year to the Holy See to make - made it possible for him to develop advanced ideas of a government. The conference, which was held in Whitland 945, was a kind of parliament in which was discussed and written Welsh law. After the death of Hywel DDAS his kingdom disintegrated rapidly into three kingdoms; Gwynedd was taken over by the sons of Idwal Foels, and Deheubarth was divided among Hywels sons. Hywels laws were fully up to the English conquest of Wales and were completely abolished in the 16th century by the English Parliament.