Mortimer is an English nobleman captured in battle by Glendower, whose claim to the throne is better than Henry IV’s.
The King refuses to believe that he did not go over to the Welsh willingly, possibly as an excuse to be rid of a rival. Mortimer is descended from an older branch of the royal family than Henry IV, and was proclaimed heir to the throne by Richard II, whom the King took the throne from. Now married to Glendower’s daughter, he is persuaded to join the rebellion against Henry IV. His marriage is somewhat marred by the fact that his wife only speaks Welsh and he only speaks English. He is not present at the battle between the rebels and the King, though the latter ends the play promising to go fight against him. How he spends the rest of his life can be discovered in Henry VI, Part One.