E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A Welsh chief, one of the most active and formidable enemies of Henry IV. He was descended from Llewellyn, the last of the Welsh princes. Sir Edmund Mortimer married one of his daughters, and the husband of Mortimers sister was Earl Percy, generally called Hotspur, who took Douglas prisoner at Homildon Hill. Glendower, Hotspur, Douglas, and others conspired to dethrone Henry, but the coalition was ruined in the fatal battle of Shrewsbury. Shakespeare makes the Welsh nobleman a wizard of great diversity of talent, but especially conceited of the prodigies that announced his birth. (Shakespeare: 1 Henry IV.)