glen'door, (1359 ?-1416 ?), a distinguished figure in Welsh history, the leader in the revolt against Henry IV of England. He had been a follower of Henry of Lancaster before his accession to the throne as Henry IV, but for personal reasons he turned against him later, and the Welsh, who had been devoted to Richard II, were very ready to follow his example. Having raised a considerable force, Glendower caused himself to be proclaimed prince of Wales in 1400. He defeated the kings' troops and, retiring to the mountains, successfully resisted for a time all attempts to bring him to action. His fortunes waned after several years, and from 1416 nothing is heard of him.