Wikipedia lists six people named Roger Mortimer, all of whom lived in the 13th and 14th centuries. The first was one of the 'marcher lords' – the barons who effectively controlled the lands around the English–Welsh border in Norman times; his home was at Wigmore Abbey in Herefordshire.
The second Roger Mortimer was the son of the first, and was the one that opposed Simon de Montfort in support of Henry III. He lived from 1231 to 1282, and was created Baron Mortimer of Wigmore.
The 2nd Baron Mortimer was his eldest son, Edmund Mortimer. (The third Roger Mortimer was the second son of the 1st Baron, and was created Baron Mortimer of Chirk.)
The one who plotted against Edward II was the 3rd Baron Mortimer – the son of the 2nd Baron, and grandson of the 1st. He is the fourth of Wikipedia's six Roger Mortimers. He was created Earl of March in 1328, but the title was forfeited in 1330 (the year he was executed for treason). His grandson (Wikipedia's fifth Roger Mortimer) managed to get the title restored in 1348, becoming the 2nd Earl of March; his grandson, the 4th Earl (Wikipedia's sixth Roger Mortimer) was heir presumptive to King Richard II, through his mother – Philippa, 5th Countess of Ulster, who was the granddaughter of Edward III and thus Richard's first cousin. The 4th Earl died in battle in Ireland in 1398, whereupon the title passed to his six–year–old son, Edmund. Any ambitions of monarchy that the 5th Earl of March may have had were of course dashed, however, when Richard was deposed by another of his cousins, Henry Bolingbroke – who thus became King Henry IV.
The 5th Earl of March married in 1415, at the age of 14, but died ten years later from plague, having left no heirs. The title passed to Richard Plantagenet, Duke of York, who passed the title on to his son Edward. The 7th Earl would later become King Edward IV, causing the earldom of March to merge into the Crown.
The title Earls of March was in fact first granted in Scotland. The Earls of Lothian (also known as Earls of Dunbar) had used it since at least 1242, but it was forfeited in 1435 by the 11th Earl. Since then it has had a complicated history, being recreated three times in Scotland and three times in England. As far as I can make out, the last person to hold the English title was Charles Henry Gordon–Lennox (born 1955), the owner of the Goodwood Estate, who is also the 11th Duke of Richmond, 11th Duke of Lennox, 11th Duke of Aubigny, and 6th Duke of Gordon. He is still alive, but seems to have relinquished this particular title in 2017. Well ... it's not as though he's short of titles.
There is still an Earl of March in Scotland: he is James Donald Charteris, 13th Earl of Wemyss and 9th Earl of March (born in 1948).
© Haydn Thompson 2021