He is a prominent character in the romantic stories of Geoffrey of Monmouth, where he is portrayed as the last in an ancient line to hold the title King of Britain.

He renounces his throne in 688 to become a pilgrim, in response to a prophecy that his sacrifice of personal power will bring about a future victory of the Britons over the Anglo-Saxons.

[2] It was also used by both the Yorkist and Lancastrian factions during the Wars of the Roses to claim that their candidate would fulfil the prophecy by restoring the authentic lineage stemming from Cadwaladr.

Cadwaladr's name is invoked in a number of literary works such as in the Armes Prydein, an early 10th-century prophetic poem from the Book of Taliesin.

"[18] According to Elissa R. Henken, Cadwaladr was well established as a "prophesied deliverer" of the Britons before Geoffrey's version of his life altered its ending.

"[18] Cadwaladr figures prominently in Geoffrey of Monmouth's romantic account of the Historia Regum Britanniae (English: History of the Kings of Britain).

In Book XII, Chapter XIV of the Historia, Cadwaladr is given as the last in a line of kings that began with Brutus of Troy.

At the same time, in Brittany, Cadwaladr intends to return to take back the island and asks Alan to provide him with an army.

The Breton king agrees, but Cadwaladr hears a prophetic voice which tells him that he must sacrifice personal power for the sake of his people.

His son Ivor and his nephew Ynyr return to Britain with an army, but, as predicted, are not successful in restoring British control of the island.

Edward IV claimed to be restoring the authentic ancient lineage of Cadwaladr, thus fulfilling Merlin's prophecy of the victory of the Red Dragon.

His chancellor gave a sermon asserting that "the British line, which perished with Cadwallader's exile in 689 was restored by the arrival of Edward the king prophesied by Merlin and others.

When Henry Tudor landed in Wales in 1485, he adopted the Red Dragon flag and claimed to be returning in fulfilment of the prophesies of Merlin as recorded by Geoffrey of Monmouth.

After his victory at the Battle of Bosworth Field Henry was greeted at the gates of Worcester with a poem asserting: Cadwallader's blood lineally descending, Long hath be told of such a prince coming.

[2] Raphael Holinshed summed up the English view in his 1577 Chronicles of England, Scotland, and Ireland: But herein appeareth the error of the British writers in taking one for another, by reason of resemblance of names, for where Ceadwalla king of the Westsaxons about that time moved of a religious devotion, after he was converted to the faith, went unto Rome, and was there baptised, or else confirmed of the foresaid Pope Sergius I, and shortly after departed this life in that city in the foresaid year of 689 or thereabouts.

The Welshmen count him to be their Cadwallader: which to be true is very unlike by that which may be gathered out the learned writings of divers good and approved authors.

[26]Also traced to Geoffrey's fertile imagination are stories of Ivor ap Alan and Ynyr travelling from Brittany to Britain.