In the early years of Wales, there were as many as 18 separate princedoms within the 8,000 square miles of Wales, largely because the Welsh law of portion, gavelkind, divided inheritances equally among all a man's sons, and so fragmented kingdoms as well as farms. They often fought against each other, besides being engaged in interminable warfare with their enemies. Between 949 and 1045, according to the 13th century Brut y Tywysogyn, the Chronicle of Princes, 35 of their rulers died by violence and 4 more were forcibly blinded.

Weis' "Ancestral Roots. . ." (176:1). Bartrum's "Welsh Genealogies". Owain became King of Deheubarth upon the death of his father HYWEL in 950. It was at his requst that the Welsh genealogies and the Annales Cambriae were compiled. Owain's son, EINON, predeceased him in 984, but became the ancestor of the future line of rulers of Deheubarth. Meanwhile, the kingdom passed to his other son, MAREDUDD upon his death in 986.

Owain ap Hywel Dda, King of Deheubarth was a man of historical interests. A great deal of genealogy and the Annales Camriae were compiled at his request. Died in 988 Owain ap Hywel Dha married his second cousin Angharad Ferch Llewelyn, Queen of Powys.

http://en.wikipedia.org/wiki/Owain_ap_Hywel_Dda
Owain ap Hywel (died c. 987) was king of Deheubarth in south Wales and probably also controlled Powys. Owain was one of the three sons of Hywel the Good. Upon Hywel's death around 950, Owain, Rhodri, and Edwin divided his lands among themselves according to Welsh law. The sons were not able to retain Hywel's hegemony over Gwynedd, which was reclaimed for its earlier dynasty by the sons of Idwal Foel.
In 952, two of the sons of Idwal Foel, Iago and Ieuaf, invaded the south, penetrating as far as Dyfed. The sons of Hywel retaliated by invading the north in 954, reaching as far north as the Conwy valley before being defeated at Llanrwst and being obliged to retreat to Ceredigion.
Rhodri died in 953 and Edwin in 954, leaving Owain in sole possession of Deheubarth alone. Owain did not again try to reclaim Gwynedd; instead, he and his son Einion turned eastwards to attack the kingdom of Morgannwg (modern Glamorgan) in 960, 970, and 977. Owain was now aging, and it appears that Einion took over the rule of the kingdom on behalf of his father. On a further raid on the east in 984, Einion was killed by the noblemen of Gwent.
Following Einion's death, Owain's second son Maredudd took over his position. In 986, he successfully returned to the north and seized Gwynedd, ousting Ieuaf's son Cadwallon. The following year Owain died and Maredudd became king of Deheubarth as well, although he later consented to share his kingdom with Einion's heirs Edwin and Cadell.
The A text of the Annales Cambriae were apparently compiled at Owain's instigation.