In the later version of his legend, he possesses superhuman strength connected to a day and night cycle, adding to his already outstanding martial prowess and making him an invincible swordsman around noon, when the sun is at its height.

His character turns markedly ignoble in the Post-Vulgate Cycle, and even outright villainous in the Prose Tristan, resulting in his conflicting characterization in Le Morte d'Arthur.

Two important plotlines shed light on Gawain's redefined characterization: his being a leader in the family blood feud against the clan of King Pellinore and his initially close friendship with another great knight, Sir Lancelot, which becomes a bitter rivalry when he seeks vengeance for the death of his brothers.

In this tradition, featured in Le Morte d'Arthur, Gawain's sinful ways and his unforgiving nature inadvertently lead to the fall of Arthur and the Round Table, and ultimately his own death by Lancelot's hand.

; in Old French (and sometimes English) primarily as Gavain (Gavaine) and also as Gauvain (Gauvaine), Gauvan (Gauvayn), Gauven (Gauvein/Gauveyn), Gavan (Gavane) or Gavayn (Gavayne); in Middle High German as Gâwein or Gâwân; in Italian dialects as Gavino, Galvagin or Galvano; in Old Spanish as Galván; in Old Portuguese as Galvam or Galvão; and in Middle English also as Gawaine, Gawan (Gawane), Gawayn (Gawayne), Gawein (Gaweine), Gaweyn (Gaweyne), Gauwein (Gauweine), Gauweyn (Gauweyne) or Wawen (Wowen), among many other forms and spellings.

[6][7] Lauran Toorians proposes that the Dutch name Walewein (attested in Flanders and France c. 1100) was earliest, suggesting it entered Britain during the large settlement of Flemings in Wales in the early 12th century.

[20] A similar motif was mentioned by the 16th-century Welsh scholar Sion Dafydd Rhys in an unrecorded oral tale in which Gwalchmei destroyed three evil witch-sisters, wives of the giants previously slain by Arthur, killing them within their castles through his cunning, as they could not be defeated otherwise, due to their powers.

William of Malmesbury writes, in his Gesta Regum Anglorum of around 1125, that "Walwen's" grave had been uncovered in Pembrokeshire hundreds of years after his death, following the 11th-century Norman conquest of England.

William recounts how Arthur's nephew, a renowned Post-Roman Briton soldier celebrated for his bravery, tirelessly fought against the Saxons led by Hengest's brother: "He deservedly shared in his uncle's praising, because he prevented the fall of his collapsing country for many years."

William also noted uncertainty regarding the manner of his death: "There, as certain people claim, he [Walwen] was wounded by his enemies, and cast forth from a shipwreck; by others, it is said that he was killed by his fellow citizens at a public feast.

Geoffrey mentions that Gawain was twelve years old at the time when King Lot and Arthur began a war with Norway, and that he had previously served Pope Sulpicius in Rome.

The Norman version by Wace, the Roman de Brut, ascribes to Gawain the chivalric aspect he would take in later literature, wherein he favours courtliness and love over martial valor.

[36] He is cited in Robert Laneham's letter describing the entertainments at Kenilworth in 1575,[37] and the recopying of earlier works such as The Greene Knight suggests that a popular English tradition of Gawain continued.

When Guinevere is sentenced to burn at the stake and Arthur deploys his best knights to guard the execution, Gawain nobly refuses to take part in the deed, even though his brothers will be there.

Following his death, Gawain also appears in Arthur's dream vision to tell him to wait thirty days for the reconciled Lancelot to return to Britain before fighting Mordred.

The surviving Gawain also features in the earlier French epic poem La Bataille Loquifer [fr], appearing together with Arthur and Morgan in Avalon, where they are all still alive hundreds of years later.

In De Ortu Waluuani, the young Gawain, trained as a Roman cavalry officer, undertakes a duel to determine whether Rome or Persia should possess Jerusalem.

[40] The Prose Lancelot describes Gawain as the most handsome of his brothers and notably gracious towards poor people and to societal outcasts such as lepers; the one time when he fails to properly greet an unknown maiden (Viviane) while on a quest to learn the fate of Merlin in the Vulgate Merlin Continuation, she curses him with a spell that turns him into a hideous dwarf, but later restores him to his real form after he passes a test to save her from an apparent rape in an arranged "damsel in distress"-style scenario.

[42][43][44] The Post-Vulgate narration tells how, in great part due to his supernatural strength, there have been only six knights whom Gawain failed to defeat in a sword fight: Lancelot, Hector, Bors, his own brother Gaheris (replaced with Percival by Malory), Tristan, and Morholt.

[49] This undertone of homoeroticism between Gawain and Sir Bertilak underscores the strength of male homosocial bonds, and the fact that sex never occurs reinforces ideals of the masculine chivalric code.

Here, Gawain is blamed for his irreligion and is shown to indulge in rather purposeless killing: as, for example, when he mortally wounds his relative and a fellow Knight of the Round Table, Yvain the Bastard, in one of the many random jousting duels for no particular reason (failing to even recognise him until it is too late).

In a symbolic later scene, it is her son and the new destined Grail hero, the blessed virgin knight Galahad, who will draw the sword in the stone at Camelot, after Gawain failed in the task.

The Guiron le Courtois section of Palamedes explains Gawain's many great cruelties being caused by his grief at being surpassed by other knights after not regaining his full strength following the war with Galehaut.

Such a new popular image originating in the late Old French romance tradition prompted the historical audience of The Wife of Bath's Tale to identify the story's rapist-knight character as Gawain.

Ultimately, it may be this unusual capacity for character development, rooted in but not limited to his familial relationship with Arthur, that has made Gawain such a prominent figure in the Arthurian pantheon.

Thomas Malory credits Gawain with three sons through the Lady of Lys, a sister of Bran de Lys/Lis (or "Brandles" in the Middle English The Jeaste of Syr Gawayne[57]); they are named Florence, Lovell, and Gingalain.

[46][62] The mother of Gawain's son in Wigalois is known as Florie, likely another version of Lorie from Rigomer; she also appears as Floree, daughter of King Alain of Escavalon, in the Livre d'Artus.

Arcade is renamed as Lady Ettarde in Malory's version with no happy end for her; his Le Morte d'Arthur also mentions Gawain having once been in the power of the lustful witch Hellawes.

[70] In contrast, Thomas Berger's Arthur Rex (1978) portrays Gawain as open-minded and introspective about his flaws, qualities that make him the Round Table's greatest knight.

[73] Gawain is a major character in The Squire's Tales series by Gerald Morris, in which he is portrayed as a skilled knight, immensely loyal to Arthur, and an intelligent, kind-hearted, and occasionally sarcastic.