Roger de Mortimer, 4th Earl of March, 6th Earl of Ulster (11 April 1374 – 20 July 1398) was an English nobleman. He was considered the heir presumptive to King Richard II, his mother's first cousin. Roger Mortimer's father, the 3rd Earl of March, died in 1381, leaving the six-year-old Roger to succeed to his father's title. Roger was placed under the wardship of Thomas Holland, 2nd Earl of Kent and eventually married Holland's daughter Alianore. During his lifetime, Mortimer spent much time in Ireland; he served several tenures as Lord Lieutenant of Ireland and died during a battle at Kellistown, Co. Carlow. He was succeeded by his young son, Edmund Mortimer, 5th Earl of March.