He helped his father to extend the power of Gwynedd and as king
          himself he consolidated his hold on Church and State in North Wales
          and exploited English dissensions to advance into Ceredigion; he even
          had authority later as far east as the Dee. His only major reverse was
          at Henry II's hands in 1157, after which Owain acknowledged English
          overlordship over Gwynedd. Ambitious, farsighted yet prudent, Owain
          was much lauded as the pre-eminent ruler in Wales.
 

Source: Leo van de Pas