Origins and Names
Dragons were Morgoth's own device, shaped in the deep places beneath Angband as part of the same secret husbandry that had already produced his orcs and werewolves, and kept hidden through long years so that even the watchful Noldor did not guess what was being bred there. When the first of that brood finally showed itself before the gates, it was still young and had not come to its full growth; the riders of Fingon met and drove it back underground before it could work great harm, and it was left to grow further in size and cunning before it dared the open field again.
The name given to this branch of the breed, Urulóki, joins Elvish words for fire and serpent and sets the flame-breathing kind apart from other creatures that came out of Angband; the same tradition names the eldest of them father of the race, the stock from which all later dragons, winged and wingless alike, were reckoned to descend. Wings were a later development within the line: only some generations after the first crawling drakes did fully winged dragons appear, larger and more terrible than their forebears, though still counted of the same Urulóki kin.
In the telling handed down to later ages, the word 'dragon' renders the name uniformly, but an older, homelier term, 'worm', runs alongside it throughout the tales of the Third Age, an archaic word for serpent kept in use for these fire-breathing kin long after it had fallen out of ordinary speech elsewhere. By that age the race had also divided in kind: cold-drakes, wingless and without fire but strong and cunning, spread out of the north around the Withered Heath and drove the Dwarves from their halls, while the rarer fire-drakes, breathing flame and sometimes winged, were remembered as the mightier and more dreaded of the two.
History
The breed came into its true strength only after Glaurung had grown to full size and dared the open field again; he led the armies of Angband in the Battle of Sudden Flame, and the fire that poured before him broke the long Siege of Angband that the Noldor and their allies had held for centuries. That defeat opened Beleriand to Morgoth's forces for the rest of the age and marked the point at which dragons ceased to be a rumor of the north and became a standing weapon of war, deployed at the head of armies rather than kept as a curiosity beneath the mountains.
Glaurung's dragons broke the allied ranks again in the Nírnaeth Arnoediad, scattering the Men of Brethil and driving a wedge between the Elvish and Mannish hosts at the battle's crisis. Years afterward Glaurung himself descended alone upon Nargothrond, overthrew its bridge and drove out its people, and settled upon the plundered hoard, laying a spell of forgetting and false counsel upon Húrin's daughter Nienor and working the ruin that fell upon Túrin and his kin; he was slain at last by Túrin's blade at the ravine of Cabed-en-Aras, the one deed by which Morgoth's eldest dragon was brought down within the tale of Beleriand.
The race reached its greatest number and size only at the very end of the age, when Morgoth loosed a host of winged dragons against the assembled fleets and armies of the War of Wrath, foremost among them Ancalagon the Black, reckoned the mightiest of all his winged kind. That assault broke against the newly arrived power of Eärendil and the Eagles of Manwë; Ancalagon was cast down upon the towers of Thangorodrim, shattering them, and the greater part of the winged dragons perished with him or fled, so that the breed that had ruled the skies over Beleriand for a season was all but ended in a single battle.
Those few dragons that survived the fall of Angband withdrew into the far north, and through the Second and Third Ages the line lingered in small numbers around the Withered Heath, occasionally rousing to trouble the Dwarven realms nearby. In the Third Age a cold-drake out of the north descended upon the Dwarves of the Grey Mountains and slew King Dáin I before his own doors, and the harrying of that stock afterward pressed the surviving Dwarves to abandon the Grey Mountains altogether and seek out Erebor and the Iron Hills instead.
The most storied of the later fire-drakes, Smaug, came down upon Erebor and Dale in the following century, killed or scattered their people, and lay for long years upon the plundered wealth of Thráin's line, so that the Lonely Mountain passed from a Dwarf-kingdom into a single dragon's hoard. He was roused from that hoard by the burglary arranged for Thorin Oakenshield's company, and in the rage that followed he fell upon Lake-town, where the bowman Bard slew him with a black arrow, ending the last dragon-conquest of a Dwarf-kingdom remembered in the tales of that age.
By the time of the War of the Ring no dragon of any account remained in the world, and those who spoke of them at all, even among the wise, treated them as a wonder of vanished ages rather than a present danger; Gandalf could remark that the North had been free of dragon-fire for many lifetimes of Men, and younger folk such as the Shire-hobbits knew the great worms only as figures out of old nursery-tales. The breed that had once broken sieges and swallowed kingdoms had thus dwindled, within little more than an age of the world, to a memory kept alive chiefly in songs and warnings.
Ways and Works
Dragons speak, and their speech is itself a weapon alongside fire and poison. They favor boastful, riddling talk, drawing a visitor out with flattery and half-truths in order to probe for weakness, coax out names and secrets, or plant doubt and despair; such talk works almost as an enchantment on the hearer, so that meeting a dragon's tongue is reckoned nearly as dangerous as meeting its claws. This guile sets them apart among Morgoth's creatures as reasoning, deliberate malice rather than mere beasts driven by hunger or rage.
What a dragon seizes, it keeps: it settles upon a captured hoard and lies unmoving atop it for years or generations, adding little and spending less, until its wealth becomes almost inseparable from its own hide, the underside said to gather a crust of gold-dust and gems pressed into the flesh by long lying upon treasure. That same hoard-hunger proves contagious, for those who covet a dragon's plunder, even after the beast itself is dead, are prone to the same possessive madness, a folly remembered afterward as dragon-sickness among those who handled such treasure. For all their armored bulk, a dragon's underside commonly keeps some bare or thinly scaled patch, a single vulnerable point that a keen eye or old counsel might find and a well-aimed shot exploit.
Dragons are reckoned to live and grow for centuries, adding bulk, cunning, and reach of flame the longer they endure, so that age alone made the eldest among them far more formidable than young drakes newly out of the pits where they were bred. They kept no fellowship, built nothing, and raised no following of their own; each lived and hunted alone, answerable only to the dark power that had bred or inherited it, deployed as a living weapon rather than as a people with laws or dwellings of its own. The tales grant them no rite or reverence in death either: a slain dragon is simply a monster brought down, its hoard passing to whoever can claim it, without the mourning or memorial that Elves, Men, or Dwarves kept for their own dead.
In the Story
Within The Hobbit, the meeting with Smaug is built as a set-piece of wit rather than combat: Bilbo descends into the dragon's lair unarmed and talks his way past a creature he cannot hope to fight, trading riddling names and flattery in a scene that deliberately echoes his earlier contest with Gollum. The exchange functions as a measure of how far the once-reluctant burglar has grown, and it is Smaug's vanity, teased out by Bilbo's careful questions, that yields the one piece of intelligence the story needs to bring the dragon down. The dragon here stands less as a monster to be slain by the hero than as an obstacle a small, clever person must outthink, and the tale's real climax, Smaug's death over Lake-town, happens offstage, delivered to an archer rather than to Bilbo at all.
In Glaurung the same breed serves a darker narrative purpose, that of an intelligence working the ruin of a family rather than a beast overrunning a field. His deceptions of Nienor and Túrin drive the story's central reversals not through force but through lies planted at the right moment, so that the dragon becomes the instrument by which Morgoth's malice reaches into private grief and memory long after open war has failed to break the house of Hador. The tale keeps Glaurung's cunning and Túrin's pride locked together, so that the dragon reads less as an external threat than as the shape Túrin's own doom finally takes.
By the time the story reaches the Shire, dragons have receded into exactly the kind of half-believed fireside tale that Bilbo once lived through, and the narrative uses that distance for its own effect: when Sam Gamgee's fondness for old dragon-lore comes up in conversation, his father dismisses it as harmless nonsense, unaware that his own family produced the hobbit who spoke with one. The joke depends on the gap between what the wider world now treats as invented wonder and what the story's own history has already shown to be true, and it quietly signals that the age of dragons, though closed, is not so distant as the Shire supposes.
Drafts and Variants
In the earliest form of the legend, told as "Turambar and the Foalókë" in the Book of Lost Tales, the dragon of Nargothrond bore the name Glorund rather than Glaurung, and the tale's title itself preserves an early generic term for his kind: Foalókë, a word for a hoard-guarding serpent that stood alongside, and eventually gave way to, the name Glaurung and the later collective term Urulóki. The dragon's essential role in ruining Túrin's family was already present in this earliest telling, but the vocabulary for naming both the individual beast and the race as a whole was still unsettled, and Christopher Tolkien's notes trace how Glorund was gradually replaced by Glaurung as the legend was rewritten in later prose and verse.
The Lost Tales version of the fall of Gondolin also shows a conception of dragons markedly different from the wholly living creatures of the later Silmarillion: alongside true fire-breathing worms, Melko's assault employs dragons of bronze and iron, artificial or part-mechanical serpents strong enough to be ridden or to serve as engines of war against the city's defenses. This idea of manufactured, metal dragons fighting beside the biological Urulóki was not carried forward into the mature legendarium, where all dragons, whatever their kind, are consistently Morgoth's bred and living creatures rather than devices built by his smiths.