Glendower, Or Glendwr Owen, a Welsh chieftain, born in Merionethshire about 1349, died Sept. 20, 1415. His father was Gryffydd Vy-chan, and his mother, Elena, was granddaughter of Llewellyn, the last Welsh prince of "Wales. He studied law at the inns of court in London, and became a barrister, but soon quitted the profession for that of arms. He was made squire of the body to Richard II., to whom he adhered throughout his disastrous reign. In 1387 he was knighted, and at an early age married Margaret, daughter of Sir David Hanmer. After the deposition of Richard II., he retired to his lordship of Glen-dwrdwy in Wales. His retirement was wrongfully construed into disloyalty to the new king Henry IV., and his estates were declared forfeited, and seized by Lord Grey de Ruthyn, an Anglo-Norman nobleman whose domains adjoined those of Glendower. Glendower then proclaimed himself prince of Wales, and called his countrymen to arms. The Welsh bards espoused the cause of Glendower, and he was soon at the head of a considerable force of enthusiastic partisans. In the summer of 1400 he seized the estates of Lord Grey. That nobleman in reprisal, with the help of Lord Talbot, who had been sent to his assistance by the king, surprised the residence of Glendower, who narrowly escaped capture.

Rallying his followers, he pillaged and burned the town of Ruthyn, and made such progress that the king in person took the field against him. A long contest ensued, in the course of which Glendower in 1402 made prisoner his old enemy Lord Grey, whom he compelled to pay a ransom of 10,000 marks and to marry his fourth daughter, Jane; he also captured Sir Edward Mortimer, but treated him with such kindness that he became Glendower's partisan, and arranged for him an alliance with the Percys of Northumberland. The confederates agreed to divide the kingdom among themselves. Glendower then called together the estates of Wales, and was formally crowned prince at Machynlleth. In 1403 the confederates gave battle to Henry near Shrewsbury, and were defeated, Percy being killed. Glendower in 1404 entered into alliance with France, and gained some victories; but in March, 1405, he was defeated at Grosmont castle and at Mynydd pwl Melyn, losing 2,300 men. He wandered about, hiding himself in woods and caves, until the French king sent him 12,000 men, to whom Glendower joined 11,000 Welsh, and marching into England, penetrated as far as Worcester. But after several indecisive engagements the allies retreated into Wales, and shortly afterward the French returned to their own country.

For some years Glendower waged a partisan and predatory war, and at the time of his death was negotiating with Sir Gilbert Talbot, who had been sent by Henry V. to offer him and his followers a free pardon. Glendower had five daughters and several sons, most or all of whom fell in battle in 1400.