Owain, the eldest son of Cadwgan ap Bleddyn, prince of part of Powys,is first recorded in 1106, when he killed Meurig and Griffri, the sons of Trahaearn ap Caradog, who held lands in Arwystli.

Owain's father Cadwgan in 1109, had given a great feast at his court in Ceredigion, and at this feast Owain was told of the beauty of Nest, whose husband Gerald of Windsor holds the castle of Cenarth Bychan (possibly Cilgerran Castle).

He had decided to visit Cenarth Bychan to see for himself, and having done so fell in love with Nest and determined to have her.

Owain and fifteen companions one night at Christmas 1109 burrowed underneath the gate to get into the castle then rushed in to abduct Nest and her children and set fire to the castle.

Her husband, Gerald, had fled through a garderobe.

Owain's actions lead to his father being confronted with an invasion, as the justiciar of Shropshire, Richard de Beaumais, has promised the members of the cadet branches of the ruling house of Powys extensive lands if they will attack Cadwgan and Owain.

Owain had fled to Ireland while Cadwgan surrendered to King Henry I of England and lost all his lands.

Ceredigion is later returned to Cadwgan, under the condition of paying a fine of one hundred pounds and promising to have nothing more to do with Owain.

Owain had soon returned to Powys from Ireland and made an alliance with Madog ap Rhiryd.

The king had responded by releasing Owain's uncle, Iorwerth ap Bleddyn, from captivity in 1110 and returning the rule of Powys to him.

Owain had been driven out of Powys by Iorwerth and retreated to Ceredigion, whence he made raids on Dyfed, selling his captives in the Irish slave markets.

He also killed a prominent member of the Flemish colony, William of Brabant.

King Henry had responded by stripping Cadwgan of all his lands and forcing him to live as an exile in England, while Owain again fled to Ireland.

However Iorwerth had been killed by Owain's ally Madog ap Rhiryd in 1111 and the rule of Powys was returned to Cadwgan, who was allowed to recall Owain.

When Cadwgan was also killed by Madog the same year, Owain had become ruler of much of Powys.

He employs his uncle Maredudd ap Bleddyn as penteulu (captain of the guard), and in 1113 Maredudd is able to capture Madog ap Rhiryd and send him to Owain.

Owain takes vengeance for the killing of his father by blinding Madog.

The situation in Wales is meanwhile deteriorating.

Henry had conducted a campaign in South Wales in 1108, pushing out royal power in the region and colonizing the area around Pembroke with Flemings.

Some of the resident Norman lords are under attack by 1114, while in Mid-Wales, Owain ap Cadwgan has blinded one of the political hostages he is holding, and in North Wales Gruffudd ap Cynan threatens the power of the Earl of Chester.

In an attack mainly aimed against Gruffydd ap Cynan, Henry sends three armies into Wales this year, with Gilbert Fitz Richard leading a force from the south, Alexander, King of Scotland, pressing from the north and Henry himself advancing into Mid-Wales.

Owain and Gruffudd sue for peace, and Henry accepts a political compromise.

Henry reinforced the Welsh Marches with his own appointees, strengthening the border territories.

After peace terms have been agreed, Henry takes Owain with him when he visits Normandy later this year and knights him.

Nest had borne Owain two sons, Llywelyn and Einion, before eventually being returned to her husband Gerald of Windsor.

Owain returns with the Henry in 1115 and in 1116 takes to arms to assist the king in putting down the rebellion of Gruffydd ap Rhys of Deheubarth.

Gerald, who is fighting on the same side, takes the opportunity for vengeance, attacking Owain when he has only ninety men with him and killing him.

Most of Powys now passes to his uncle, Maredudd.