Idwal Iwrch (English: Idwal the Roebuck), or Idwal ap Cadwaladr (English: Idwal son of Cadwaladr), is a figure in the genealogies of the kings of Gwynedd. He was the son of King Cadwaladr ap Cadwallon (reigned c. 655 – 682) and the father of King Rhodri Molwynog (died 754). The records of this era are scanty, and Idwal's name appears only in the pedigrees of later kings and in a prophecy found in two 14th-century Welsh manuscripts, which says that he will succeed his father Cadwaladr as king.
The only mention of Idwal Iwrch in the historical record is the appearance of his name in genealogies such as those from Jesus College MS. 20 (as the father of "Rhodri Molwynog son of Idwal Iwrch son of Cadwaladr Fendigiad") and the Harleian genealogies (as the father of "Rotri son of Intguaul son of Catgualart"). John Davies' History of Wales does not mention Idwal, while John Edward Lloyd's History says only that Idwal was Rhodri Molwynog's father. The King of Gwynedd during Idwal's lifetime is not known, and while he is one of the most likely candidates (because he was both the son of a king and the father of a king), there is no sufficiently reliable basis to either assert or deny it.
Idwal's name appears in the Dialogue between Myrddin and his sister Gwenddydd (Welsh: Cyfoesi Myrddin a Gwenddydd ei chwaer), a Middle Welsh vaticinatory poem whose text is preserved in two medieval Welsh manuscripts, Peniarth 3 (c. 1300) and the Red Book of Hergest (c. 1380-1410). In the text's question-answer form, a succession of "future" kings is prophesied, with Idwal among them. This succession agrees with the historical genealogies from father to son, but does not agree with the known royal succession.
- Phillimore, Egerton, ed. (1887), "Pedigrees from Jesus College MS. 20", Y Cymmrodor, VIII, Honourable Society of Cymmrodorion, pp. 77–92; the pedigree is given as: ... Cynan tintaeth6y. M. Rodri mol6yna6c. M. Idwal I6rch. M. Kadwaladyr vendigeit. M. Katwalla6n. M. Kad6ga6n. M. Iago. M. Beli. M. Run hir. M. Maelg6n g6yned ..., and from there back to Cunedda.
- Phillimore, Egerton (1888), "The Annales Cambriae and Old Welsh Genealogies, from Harleian MS. 3859", in Phillimore, Egerton, Y Cymmrodor, IX, Honourable Society of Cymmrodorion, pp. 141–183; on pages 169 – 170 the pedigree is given as: ... map Rotri map mermin map etthil merch cinnan map rotri map Intguaul map Catgualart map Catgollaun map Catman ..., and from there back to Cunedda and his ancestors.
- Davies, John (1990), A History of Wales (First ed.), London: Penguin Group (published 1993), ISBN 0-7139-9098-8
- Lloyd, John Edward (1911), A History of Wales from the Earliest Times to the Edwardian Conquest, I (2nd ed.), London: Longmans, Green, and Co (published 1912), p. 231
- Meic Stephens (ed.), Cydymaith i Lenyddiaeth Cymru (University of Wales Press, revised edition 1992), p. 105.
- Jones, Mary. "The Dialogue Between Myrddin and His Sister Gwenddydd". maryjones.us. Retrieved September 11, 2009. — for example, Cadwallon was the father of Cadwaladr, but Cadafael followed Cadwallon in the royal succession and Cadwaladr followed Cadafael, not as the prophecy claims.