The daughter of Prince of Gwynedd Gruffudd ap Cynan and member of the House of Aberffraw, she married Gruffydd ap Rhys, the Prince of Deheubarth, and would lead a "patriotic revolt" with him during the Great Revolt of 1136 until her death at the battle at Kidwelly Castle.
Gwenllian was the youngest daughter of Gruffudd ap Cynan, Prince of Gwynedd, and his wife, Angharad.
While the conflict between the Normans and the Welsh continued, the princely family were often displaced, with Gwenllian joining her husband in mountainous and forested strongholds.
[3] From here, she and Gruffydd ap Rhys led retaliatory strikes, aka "lightning raids" against Norman-held positions in Deheubarth.
[3] By 1136 an opportunity arose for the Welsh to recover lands lost to the Marcher Lords when Stephen de Blois displaced his cousin, Empress Matilda, from succeeding her father to the English throne the year prior, sparking the Anarchy in England.
[11] The Welsh of Gwent, led by Iorwerth ab Owain (grandson of Caradog ap Gruffydd, Gwent's Welsh ruler displaced by the Norman invasions), ambushed and slew Richard Fitz Gilbert de Clare, the Norman lord who controlled Ceredigion.
These actions led historian and author Philip Warner to described Gwenlliann and her husband as a pair of "Robin Hoods of Wales".