Mortimer, Edmund de, 5th earl of March and 3d earl of Ulster, 1391–1425, English nobleman, son of Roger de Mortimer, 4th earl of March. He succeeded (1398) his father not only as earl of March and Ulster but as heir presumptive to the childless Richard II. However, after the usurpation (1399) of the throne by the Lancastrian Henry IV, Mortimer was imprisoned, although allowed to inherit his estates. On the accession of Henry V (1413), he was released and served Henry in the French wars. He refused to countenance plots of partisans to raise him to the throne and even denounced a body of these conspirators to the king. After Henry V's death, Mortimer became (1422) a member of the regency council for the young Henry VI. In 1424 he took the post of lieutenant of Ireland, where his death by plague ended the male line of the Mortimers. His heiress was his sister Anne, whose son by Richard, earl of Cambridge, was Richard, duke of York, father of Edward IV and Richard III.
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