prince of Gwynedd in northern Wales who struggled unsuccessfully to drive the English from Welsh territory. He was the only Welsh ruler to be officially recognized by the English as prince of Wales, but within a year after his death Wales fell completely under English rule.

Although Llywelyn ap Gruffudd's grandfather, Llywelyn ap Iorwerth (d. 1240), had made Gwynedd the centre of Welsh power, the state nearly collapsed during the brief reign of his son David ap Llywelyn (1240–46). When David died in 1246, Llywelyn and his brother Owain divided the remaining territory. In 1255 Llywelyn seized Owain's lands and set out to assert once again Gwynedd's hegemony over Wales.

Taking advantage of the conflict between King Henry III of England and his barons, Llywelyn proclaimed himself prince of Wales and received the homage of the other Welsh princes (1258). In 1262 he took up arms against the English lords of southern Wales and allied himself with Henry III's chief baronial opponent, Simon de Montfort (Montfort, Simon de, Earl Of Leicester), who seized power in England in 1264. Montfort was killed in 1265, and two years later Llywelyn signed a treaty by which he recognized Henry's overlordship; in return, he was authorized to receive homage from the other Welsh princes. Nevertheless, upon the death of Henry III and the accession of Edward I (1272), Llywelyn again defied the English. Edward invaded Wales and subjugated Llywelyn in 1276–77, but in 1282 Llywelyn and his brother David raised a rebellion for national independence. The uprising collapsed soon after Edward's forces killed Llywelyn in a skirmish near Builth. David was killed in 1283.