His father was Cadell ap Rhodri (854–909), king of Seisyllwg from 872 until his death in 909, when it passed to Hywel. A few years before Cadell's death, he and Hywel had conquered the kingdom of Dyfed, and Hywel ruled a combined Seisyllwg and Dyfed, calling it Deheubarth.
Controlling a large part of Wales made Hywel a force to be reckoned with, but rather than fight the Anglo-Saxons, he made an alliance with them. Edward the Elder (King of the Anglo-Saxons from 899 to 924) and Hywel joined forces to fight Vikings. Another first for a Welsh leader was Hywel's pilgrimage to Rome in 928.
He continued an alliance with Edward the Elder's son, Æthelstan. Æthelstan wanted to rule the entire island of Britain, but Hywel's voluntary alliance or "submission" to Æthelstan meant he was not subject to attack or even scrutiny, while Æthelstan focused on conquering the territories to the north. Hywel supported Æthelstan's invasion of Scotland in 934, for instance.
When another of Edward the Elder's sons, Edmund, became king, Hywel's cousin Idwal, King of Gwynedd, took a stand for Welsh independence and raised an army against English forces in 942. Idwal was killed fighting against Edmund, and Hywel was able to prevent (with Edmund's approval) the throne of Gwynedd from going to Idwal's sons. Hywel exiled the sons and made himself ruler of Gwynedd, putting him in control of almost all of Wales.
The modern Welsh parliament, the Senedd Cymru, is housed in a building called Tŷ Hywel, which means "Hywel House." The original assembly chamber (now outgrown) is Siambr Hywel ("Hywel's Chamber"). Why is his name honored this way a thousand years after he ruled? I'll explain his impact on Welsh governance tomorrow.