The dragon that Bevis encounters is a fearsome opponent of long and complicated lineage within the story, and within the traditions of myth and storytelling, including those found in the Bible.
In my recently published essay on Fantasy or History in Bevis, I considered the way the original medieval audience for the story would have understood the importance of the dragon. I copy my conclusions here:
The dragon provides scale of challenge for Bevis different to those he has previously encountered. Like giants, dragons appear in Anglo-Saxon poetry and, as J.R.R. Tolkien observed, northern storytelling from the early medieval period onwards assigned specific characteristics to them as symbols of epic danger and greed. In the Old English Beowulf the dragon is ‘a personification of malice, greed, destruction (the evil side of heroic life)’ [Tolkien 2006, p.17], while the Maxims asserted ‘[d]raca sceal on hlæwe / frōd, frætwum wlanc’ [Sweet 1967, p. 175]. More specifically in the Germanic Volsunga saga, a dragon’s greed stems from its origin as the murderous giant Fafnir. The similarity between this dragon, confronted by the hero Sigurd or Siegfried, and the dragon Bevis confronts has long been acknowledged [Hibbard 1911]. However, in describing the origins of the dragon Bevis fights the Auchinleck redactor specifies details that give the beast Christian moral and eschatological significance. It was once one of a pair of vicious human warlords, not giants, both of whom eventually died unrepentant and were consigned to Hell. There they continued their wickedness until the Devil transformed them into dragons and sent them back to trouble the Earth again. One lodged under a bridge in Rome while the other dwelt under a cliff near Cologne, where Bevis encounters it.
Their confrontation is set in Christian contexts: Bevis has taken his sweetheart, the Saracen princess Josian, and their giant servant Ascupart to Cologne to be baptised (which he refuses). After Josian’s baptism Bevis prepares to the face the dragon. In the first encounter the dragon gapes at him ‘Ase he wolde him swolwe’ (as if he intended to swallow him) [Kölbing ed., 1885, ll. 2764]. It then kills Bevis’s horse, splits his shield and injures his shoulder with blows from its tail. In pain and thirsty, Bevis drinks from a holy well, which restores him. During the next part of the fight the dragon spits venom over him. This dissolves his armour and corrupts his skin until he looks like a ‘foule mesel’ (a foul leper). [Kölbing ed., 1885, ll. 2828]. Although leprosy was conventionally interpreted in the Middle Ages as a sign of sexual sin, Bevis is quickly healed by immersion in the water of the holy well, an action approximating baptism [Kay and Rubin eds., 1994, p. 48].
Bevis’s monstrous opponent is not the fire-breathing dragon of myth, legend and medieval chronicle [Tatlock 1933], nor is it protecting its treasure. Neither do its characteristics entirely fit with those described in the medieval Bestiary which presents dragons alongside real animals, describing their nature and attributes partly for the spiritual edification of readers. From natural and spiritual perspectives, for a medieval audience dragons teetered on the brink of disquieting reality [Eckert 2013, p. 585], as recent research confirms [Senter, Mattox and Haddah 2016]. The authoritative Bestiary declares that a dragon ‘has no harmful poison’ [Barber 1999, p. 183], asserting that its strength ‘lies not in its teeth, but in its tail, because having lost his power, the devil can only deceive with lies’ [Barber 1999, p. 183]. As Jennifer Fellows observes ‘[i]n Western cultures, under the influence of biblical symbolism, the dragon early came to be identified specifically with diabolic forces of evil, and it is as the Devil himself that it is allegorised in the bestiaries’ [Fellows 2006, p. 1]. The emphatic connection in medieval minds between dragons and devils is referenced explicitly in another romance in the Auchinleck MS, where the eponymous hero of Sir Tristrem confronts a dragon described simply as ‘þe deuel dragoun’ [McNeill 1886, l. 1446].
The biblical origins of the Devil as dragon lie in the account in the Apocalypsis Iohannis in which war in heaven ends when proiectus est draco ille magnus serpens antiques qui vocatur Diabolus et Satanas qui seducit universum orbem [Weber 1969, Apc 12: 9]. However, Bernard Spivack notes a medieval acceptance that the ‘Devil was not a personification but a concretely historical figure in the Christian mythos’ [Spivack 1958, p. 78]. More recently John D. Cox has reviewed the medieval belief in the presence of the Devil in everyday life asserting that
the devil was not supernatural; he was merely superhuman…. he was ubiquitous, because his opposition to God accounted for everything that was wrong, not merely in obvious moral or religious terms…. One of the major purposes of religious activity throughout one’s life, from baptism to the last rites, was therefore to reject and defeat the devil [Cox 2000, p. 11-16].
Although the ‘reality’ of the dragon Bevis fights may initially appear to be offset by the story of its origin and its folkloric echoes, the fact that in the Auchinleck Bevis this most potent of all monsters in western literary tradition is a demonically transformed man emphasises the thoroughly ideological correctness of the process and result of Bevis’s eventual victory.
After his conquest of the Saracen giant, the dragon fight tests and illuminates different aspects of Bevis’s character as a Christian warrior. Before the fight his motivation is questionable as he tells the cowardly Ascupart ‘Hadde we þe dragoun wonne, / We hadde þe feireste pris vnder sonne!’ [Kölbing ed., 1885, ll. 2746-7], implicitly expressing pride in the fame that would result from victory. The dragon’s attack which wounds him exposes his vulnerability to the temptation of martial glory, but after being restored from this wound and the contagion of the dragon’s venom:
On is knes he gan to falle,
To Jesu Crist he gan to calle:
“Help, … Godes sone,
Þat þis dragoun wer ouer-come!
Boute ich mowe þe dragoun slon
Er þan ich hennes gon
Schel hit neuer aslawe be
For noman in Cristenté”.
To God he made his praiere
And to Marie, his moder dere. [Kölbing ed., 1885, ll.
The dragon flees on hearing this prayer for aid, expressed in terms of the hero’s humble realisation that he is Christendom’s last line of defence [Finlayson 1999, p.384], but it does not escape, and during the ensuing fight, action focuses three times on the dragon’s mouth.
Initially it gapes, not to spout flame, but as if to swallow Bevis, reiterating the image, familiar in medieval paintings, carvings and illuminated manuscripts of the mouth of hell as the gaping maw of a dragon into which sinners are swallowed. After being contaminated by its venom and restored by the virtue of the well, Bevis attacks the dragon slicing through its ‘throte boll’, its Adam’s apple [Kölbing ed., 1885, l. 2880]. This unusual physical detail recalls the beast’s former identity as a human with the power of speech, although unlike the transformed Fafnir in the Volsunga saga, the Cologne dragon does not speak to its opponent. Once he has killed the monster, Bevis beheads it and cuts out its tongue. The removal of the tongue from this demonically transformed dragon most significantly symbolises Bevis’s disarming of the Devil’s ability to corrupt through speech. Notorious in the Middle Ages as the ‘father of lies’, the Devil was held to deceive humankind through speech [Augustine 1972, p. 445], and as Thomas Aquinas wrote in the thirteenth century: ‘the devil can cause sin only by persuasion’ [Aquinas 1989, p. 158]. The dragon’s venom therefore symbolises not the usual leprous contamination of sexual sin, but the destructive power of demonic persuasion which may be likened to leprosy in its effect on the soul. The excisions thus signify Bevis’s power to overcome the monstrous power of the Devil’s lies and incitements to sin through the aid of baptism and the power of prayer.
St. Augustine also declared that ‘sin first came into existence as a result of the Devil’s pride’ [Augustine 1972, p. 447]. The Devil as cause of sin is clearly promoted in this romance over folkloric association of dragons with greed. Because the dragon is a transformed war-lord who would not desist from conflict, Bevis simultaneously asserts the potency of prayer, and exerts control over, and rejection of, the wanton violence for which the man was initially condemned to Hell, thereby demonstrating his resistance to those demonically-induced sins, including malice and pride, that were, as Tolkien noted the inverse of the chivalric code. The manner of Bevis’s conquest of the dragon therefore defines the parameters of hegemonically acceptable chivalric violence – against spiritual and social enemies – not for personal pride in martial prowess or love of violence.
Tolkien asserted that the effect on a hero of overcoming a dragon renders him ‘[s]omething more significant than the standard hero, a man faced with a foe more evil than any human enemy’ [Tolkien 2006, p. 17]. In Bevis’s case, the transformed dragon personifies both human and demonic evil so his victory over it enhances his heroism because he withstands both through his own valour and faith strengthened by symbolic ‘baptism’ in the well. Bevis’s dragon fight is not, then, just another among many that enliven medieval romances and folk tales. It references the legend of St. George and the dragon, but the venom and the focus on organs of speech do not appear in medieval accounts of St. George [Whatley, Thompson and Upchurch, eds., 2004]. Jennifer Fellows sees Bevis’s fight as ‘in narrative terms, a completely detachable episode which bears no essential relationship to the rest of the story’ [Fellows 2008, p. 83]. On the contrary, I would argue that the form of the episode establishes Bevis’s resistance to the sins symbolised by both dragon and Devil. Bevis is not saintly but initially susceptible to a warrior’s pride in his own mastery of the arts of violence, when he overcomes, with the aid of faith, the flaws in himself that the dragon exposes as it wounds and disfigures him, this is a defining moment in a process which fits him for his ultimate task.
 Jennifer Fellows notes that C.S. Lewis echoes the transformation motif when the boy Eustace becomes a dragon in The Voyage of the Dawn-Treader [ Fellows, ‘Dragons two other thre: the dragon motif in some Middle English romances’, unpublished paper presented at the ‘Romance in Medieval Britain’ conference, University of York, 2006, p.6].
 This threat may reference the legend of St Margaret who was swallowed by the Devil in the shape of a dragon, but her virtue burst its belly.
The importance of the dragon can never be underestimated in any medieval story. Its significance continues into the early modern period and only in recent times has this been reduced to suit the expectations of popular culture in the 21st century.
The scholar and author Edmund Fairfax has summarised useful secular background information on the development of ‘dragon’ as a word and concept: