Roger de Mortimer, 1st Earl of March (25 April 1287 – 29 November 1330), grandson of the 1st Baron Wigmore, was the best-known of his name. As a result of his adulterous relationship with Isabella of France, queen of King Edward II of England, he was responsible for deposing (and probably for murdering) King Edward II, and making himself effectively the ruler of England.

He inherited (c.1304) the vast estates and the title of his father, Edmund, 7th baron of Wigmore. Appointed lieutenant of Ireland in 1316, he was instrumental in securing the defeat of Edward Bruce and thus was able to consolidate his own holdings in Ireland. His principal estates, however, were in the Welsh Marches, and he joined (1321) the other Marcher lords in opposition to Edward II and the Despensers (see Hugh le Despenser). He submitted to the king in 1322 and was imprisoned, but in 1323 he escaped to France. When Edward II's queen, Isabella, came to France in 1325, Mortimer became her lover. Together they invaded England in 1326 and routed Edward, whom they forced to abdicate (1327) and later had murdered. Having secured the crown for young Edward III , Mortimer, with Isabella, virtually ruled England and acquired great wealth. He became Earl of March in 1328.

Accused of assuming royal power and of various other high misdemeanours, he was condemned without trial and hanged at Tyburn on 29 November, 1330, his vast estates being forfeited to the crown. Mortimer's widow, Jeanne, received a pardon in 1336 and survived till 1356. She was buried beside Mortimer at Wigmore, but the site was later destroyed. They had 12 children together.