Mortimer, Roger de, 4th earl of March and 2d earl of Ulster, 1374–98, English nobleman. He succeeded (1381) his father, Edmund de Mortimer, 3d earl of March, and was brought up as a royal ward. In 1385 the childless Richard II proclaimed him heir presumptive to the throne. He came into possession of his estates in 1393, and in 1394 he went to Ireland with Richard to subdue the rebel Irish chiefs. Remaining there as lieutenant of Ireland he won some popularity with the people because of his bravery and liberality. His death in a battle with the clans of Leinster precipitated Richard II's fateful expedition to Ireland in 1399.
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