According to Weis & Sheppard, 7th edn, p 117, Ralph was son of Roger de MORTIMER who d. bef. 19 Aug. 1214, Lord Mortimer of Wigmore.
Ralph de Mortimer, in the 12th Henry III [1228], paying £100 for his relief, had livery of all his lands lying in the cos. of Gloucester, Southampton, Berks, Salop, and Hereford. This nobleman being of a marital disposition, erected several strong castles by which he was enabled to extend his possessions against the Welsh so that Prince Llewellyn, seeing that he could not successfully cope with him, gave him his dau., Gladuse Duy, widow of Reginald de Braose, in marriage, and by this lady he had issue, Roger, his successor; Peter John, a grey friar at Shrewsbury; Hugh, of Chelmersh; and a dau. Isolda, m. 1st to Walter Balem, and 2ndly, to Hugh, Lord Audley. He d. in 1246, and was s. by his eldest son, Roger de Mortimer. [Sir Bernard Burke, Dormant, Abeyant, Forfeited and Extinct Peerages, Burke's Peerage Ltd, London, England, 1883, p. 383, Mortimer, Barons Mortimer, of Wigmore, Earls of March]