Owain ap Gruffydd (c. 1359 – c. 1415), commonly known as Owain Glyndŵr or Glyn Dŵr (pronounced [ˈoʊain ɡlɨ̞nˈduːr], anglicised as Owen Glendower), was a Welsh leader who instigated a fierce and long-running war of independence with the aim of ending English rule in Wales during the Late Middle Ages. He was the first and last native Welshman to hold the title Prince of Wales (Welsh: Tywysog Cymru).Owain Glyndŵr was a descendant of the Princes of Powys through his father Gruffudd Fychan II, hereditary Tywysog of Powys Fadog and Lord of Glyndyfrdwy. Through his mother, Elen ferch Tomas ap Llywelyn he was a descendant of the Princes of Deheubarth, and through her Glyndŵr was also a descendant of Llywelyn the Great of the Gwynedd royal House of Aberffraw.On 16 September 1400, Owain Glyndŵr instigated a 15-year Welsh Revolt against the rule of King Henry IV of England. With the use of guerilla tactics, the Welsh troops managed to inflict a series of defeats on the English forces and captured key castles across Wales, rapidly gaining control of most of the country. News of the rebellion's success spread internationally across Europe and Glyndwr began receiving naval support from Scotland and Brittany, He also received the support of King Charles VI of France who agreed to send French troops and supplies to aid the rebellion. In 1403 a Welsh army including a French contingent assimilated into forces mainly from Morgannwg and the Rhondda Valleys region commanded by Owain Glyndŵr, his senior general Rhys Gethin and Cadwgan, Lord of Glyn Rhondda, defeated a large English invasion force reputedly led by King Henry IV himself at the Battle of Stalling Down in Glamorgan, South Wales.By 1404 no less than four royal military expeditions into Wales had been repelled and Owain solidified his control of the nation. He was officially crowned Prince of Wales and held a parliament at Machynlleth where he outlined his national programme for an independent Wales, which included plans such as building two national universities (one in the south and one in the north), re-introducing the traditional Welsh laws of Hywel Dda, and establishing an independent Welsh church. There were envoys from other countries including from France, Scotland and the Kingdom of León (in Spain). In the summer of 1405 four men from every commote in Wales were sent to Harlech. In the same year, he signed the Tripartite Indenture.

Despite the initial success of the revolution, in 1407 the superior numbers, resources and wealth that England had at its disposal eventually began to turn the tide of the war, and the much larger and better equipped English forces began to overwhelm the Welsh and eventually by 1409 they had reconquered most of Wales. Glyndŵr fought on until he was cornered and under siege at Harlech Castle; but he managed to escape capture by disguising himself as an elderly man, sneaking out of the castle and slipping past the English military blockade in the darkness of the night. Owain retreated to the Welsh wilderness with a band of loyal supporters; he refused to surrender and continued the war with guerilla tactics such as launching sporadic raids and ambushes throughout Wales and the English borderlands. The last documented sighting of him was in 1412 when he ambushed the king's men in Brecon and captured and ransomed a leading supporter of King Henry's. He twice ignored offers of a pardon from the new king Henry V of England, and despite the large rewards offered for his capture, Glyndŵr was never betrayed to the English. His death was recorded by a former follower in the year 1415, at the age of approximately 56.With his death, Owain acquired a mythical status along with Cadwaladr, Cynan and Arthur as a folk hero awaiting the call to return and liberate his people, "Y Mab Darogan" (The Foretold Son).Glyndŵr appears as 'Owen Glendower' in William Shakespeare's play Henry IV, Part 1.