November 9, 1376 - 1409?), was the second son of the 3rd Earl of March, and is the best-known of the various Edmumd Mortimers. A grandson of Lionel of Antwerp and thus descended from King Edward III of England, he was born at Ludlow Castle in Shropshire. Despite having a good claim to the throne (better than that of Henry Bolingbroke, he supported Bolingbroke and fought for him until captured by the Welsh rebel, Owain Glyndwr in battle. When Henry proved slow to ransom Mortimer, Glyndwr won him over and married him off to his daughter, Katherine, in 1402. They are believed to have had at least four children.
Glyndwr and Mortimer plotted with Henry Percy to depose Henry IV and divide the kingdom of England and Wales in three. However, at some time during the siege of Owen's stronghold of Harlech by the future King Henry V, Mortimer died, possibly of plague.