In some settings, dragons tend to guard hoards of treasure—typically by lying on top of it.
This trope is especially ingrained in Germanic Mythology—in fact it is hard to find a dragon in ancient Anglo-Saxon, German or Norse legends that doesn't guard gold. Curiously, there is no consensus as to why dragons do this. Justifications in-story for why a dragon sits on a hoard, including backstories of how hoard and dragon came together, vary considerably.
In some ways, hoard-guarding dragons are no different from other treasure guardians: They make sure it isn't too easy for the hero to get at a desired MacGuffin, and a heap of treasure in itself provides a convincing motivation for a hero to engage in an exciting monster-fight.
Dragons have a peculiarity, though, in that they are especially attached to gold: dragon-hoards almost always contain at least a substantial share of gold. Whatever the reasons, on average dragons show noticeably less interest in other treasures, like silver or even jewels.
People have also long noticed that dragons have no apparent use for treasure: they cannot spend, wear or process it. Dragons, it was concluded, must be pathologically avaricious and stingy—kind of like a species of compulsive hoarders with a Money Fetish. In fact, up to the 17th century, dragons were considered the emblematic representation of Greed.
One possible explanation of the origin of this trope comes from the old hypothesis about dragon legends being inspired by dinosaur fossils. Miners who were digging for gold would sometimes find dinosaur bones buried nearby, hence the association between the two. This is also believed to be the reason griffons are also sometimes associated with treasure, as they're supposedly inspired by ceratopsians, being quadrupeds with beaks. The serpentile nature of many dragons also connects them with snakes. Given the fact that many snakes live in caves, and precious minerals are most often found underground, the snake/dragon = gold connection may result from simple gilt by association.
The association of dragons with greed, combined with their preference for gold, makes that dragon hoards coincide with a certain regularity with outbreaks of Gold Fever.
Treasure-hoarding dragons, once common, became increasingly forgotten in the age of Chivalric Romance: For a Knight in Shining Armor, fighting for so mundane a reward as treasure was no longer deemed noble enough. Hence gold-hoarding dragons were largely superseded by the princess-stealing ones, until the trope was revived by Fantasy literature, especially through the influence of The Hobbit.
In more realistic settings where dragons don't exist, large reptiles may sometimes be encountered guarding treasures. Parody versions will involve dragons hoarding something other than treasure.
May involve a Treasure Room. This trope is to Pooled Funds as a waterbed is to a swimming pool.
The Jungle Book (1994): When the ruthless Captain Boone tries to loot the treasure chamber of a lost city, he is eaten by a giant python.
Reign of Fire: When the young Quinn first stumbles into where the dragon is hibernating, the walls are covered by pyrite... or possibly gold. We don't get long enough to look at it before all the burning and the death starts.
The mockumentary Dragons: A Fantasy Made Real claims that dragons are naturally attracted to shiny objects and may collect hoards of such items, more or less valuable, to allure potential mates.
In Peter Jackson's The Hobbit trilogy (as first seen in The Hobbit: The Desolation of Smaug), the dragon Smaug is sleeping inside his mountain of gold. Smaug is also able to detect that the invisible Bilbo is wearing "something golden" (the Ring), which suggests he can sense (maybe smell) gold.
In the Beast Fable"The Fox and the Dragon" by Phaedrus (c. 50 AD), a fox discovers a dragon guarding a gold hoard in an underground cavern. When the fox wonders why anyone would waste his life in this way, the dragon admits there is no point to his behaviour other than that it is what Jupiter and the Fates have assigned to him. The moral then draws an explicit parallel between human avarice and miserliness and the pointless gold-hoarding of the dragon.
Saga of the Jomsvikings speculates that a sea-serpent seen at the Norwegian coast is the ghost of the Jomsviking captain Bui, guarding two chests of gold he took with him to his watery grave.
Smaug of The Hobbit destroyed the Kingdoms of Lonely Mountain and Dale to rob the kings' treasures. He heaped them up in a vault where he spends most of his time just sleeping on it. This habit also has the advantage that the coins and gems grow into his sticky, glowing hot skin, thus providing him with additional armor. Despite the hoard's fantastical size, after guarding it for decades Smaug knows it so well that he immediately detects the loss of a single cup that Bilbo stole while Smaug was asleep.
In The Lord of the Rings, Éowyn mentions that her ancestor Fram killed "Scatha the Worm" and thus won a hoard which the dragon had robbed from dwarves.
Farmer Giles of Ham has the dragon Chrysophylax Dives ("Gold-watcher the Rich"), whose cave contains fantastical riches of all sorts. How the got all that stuff is never explained, nor does anyone ever ask.
In "The Hoard", a ballad from The Adventures of Tom Bombadil, a dragon kills a dwarf to appropriate the latter's hoard. Later the dragon faces the same treatment through a human warrior.
In The Pilgrim's Regress, "the Northern dragon is so greedy that his anxiety for his gold hardly lets him sleep".
In The Voyage of the Dawn Treader, Eustace stumbles upon a dragon's hoard while the dragon is absent. He gets greedy, falls asleep on top of it, and is transformed into a dragon himself.
In the Earthsea Trilogy, the dragons are obsessed with hoarding jewelry ... at least at first.
In Barbara Hambly's Dragonsbane series, dragons love gold because dragon magic resonates with it to produce a narcotic-like effect that dragons easily become addicted to. Some dragons manage to break this addiction, however.
Dragonology explains that dragons hoard treasure to use as armor for their soft underbelly. It also states that certain species are capable of learning to concept of value and add collector's items like rare books to their hoard out of avarice.
In Guards! Guards!, the dragon that takes over the palace of Ankh-Morpork demands all the gold for its hoard. Since Ankh-Morpork is a Vestigial Empire of gilded treasures and heavily diluted coinage, there's a lot of ugliness before the dragon is satisfied.
In the J.W. Wells & Co. series, dragons often appear in the vaults of banks, which is why companies like J.W. Wells find it useful and lucrative to keep a "pest control specialist" in their employ.
In the Myth Adventures novels, Gleep explains that dragons hoard gold because it's so soft and corrosion-proof that it's ideal for baby dragons to teethe on. Dragons with offspring collect it for their young, and grown-up dragons keep it as a sentimental reminder of childhood.
In Heir Apparent, the protagonist needs to sneak into a dragon's lair to steal its treasure.
In Age of Fire, dragons hoard because they need metal to make scales.
In The Forgotten Beasts of Eld, the dragon Gyld is old and tired and mostly content to live in Sybel's menagerie, but occasionally longs for his old hoard, which ends up causing some trouble.
John Gardner's Grendel features a dragon who hoards gold, and advises Grendel that the only point of life is to "find a pile of gold and sit on it."
A quest for a fabled Dragon Hoard (inspired by the Golden Fleece, and likewise a case of the dragon being hired to guard a royal treasure) provides the main plot in The Dragon Hoard by Tanith Lee. The trope is also parodied in a story-within-the-story that includes a dragon who can't hoard gold because he's allergic to it.
In Jo Walton's Tooth and Claw (an Anthony Trollope pastiche With Dragons!), dragons have a natural instinct to sleep on piles of hoarded gold. Unfortunately, one cannot do this and invest one's gold in the stock market at the same time.
Parodied in Grunts! by Mary Gentle: A troop of Orcs is ordered to steal powerful artifacts from a dragon hoard. It turns out the dragon was not interested in treasure, but a collector of weapons and militaria.
In Seraphina Dragons hoarded treasure until the treaty and Ardmagar Comonotï¿½s reforms. Interestingly, the new generation of dragons still hoard in a way, collecting books and sitting on them.
In Everworld, the only thing dragons seem to care about is money; Merlin has a few who works for him, and at least one argues about fees during their mission. The series' best example is Nidhoggr, who, aside from being huge even by dragon standards, has a hoard to match. Yet when the protagonists meet him, he's miserable/furious that some of it (namely, four magical items previously belonging to the Celtic gods) were stolen by leprechauns.
It was insane, of course. This dragon, this braciosaurus of a creature, was sitting in and on enough wealth to buy France. And yet, the monstrous thing was crying, weeping swimming pools of tears.
The Dragon's Ring series portrays dragons as having a psychological addiction to gold, as their hoards are not only a preeminent status symbol but magically revitalize their powers when in physical contact. The novels show that this can be taken advantage of when fighting them, such as offering them a cursed gold coin which they will be unable to resist.
In "The Tasks of Tantalon", one of the Fighting Fantasy books, one of the tasks is to steal the gold of the Brimstone Dragon.
In Dragon Slippers, dragons have hoards of things like shoes, glass windows, and live animals.
Live Action TV
Played with in the Doctor Who episode trilogy "Dragonfire" which has Mel and the Doctor go hunting for a rumored treasure that supposedly is guarded by a dragon below the surface of the ice planet Svartos. The reality turns out somewhat different.
One issue of Dragon Magazine had for its cover a picture of a dragon's hoard, which contained gold, jewels, and many, many less conventional objects, like a kitchen sink.
Dragons of Classical Mythology frequently guard something (usually on command of a god), but there is a broad range of objects guarded. It helps that dragons are often said to never sleep, making them ideal guardians. There are at least two prominent instances of dragons guarding golden MacGuffins:
The dragon Ladon was set by Hera to guard the Golden Apples that grow in the Garden of the Hesperides.
King Aeëtes of Colchis employed a large serpentine dragon to guard the Golden Fleece sought by Jason and the Argonauts.
In Rome, there was a folk belief that dragons guard buried treasure as a natural instinct, and dragons therefore are referenced as epitomes of avarice:
Invoked in Cicero's 13th Philippic Speech (delivered March 43 B.C.), when Cicero says about a henchman of Marc Antony who had appropriated part of Pompey's property that he "clutches the patrimony [of Pompey] like a dragon clutches treasure". The word Cicero uses ("circumplexus") implies that he imagines the dragon literally coiling around his treasure.
When describing a painting that showed a dragon, the Greek writer Philostratus (3rd century AD) claims that dragons are "devoted to gold", and because of this instinct may guard "treasure that lies hidden under the earth".
Chinese Mythology: The fucanglong or "hidden treasure dragon" lives underground, guarding both man-made treasure as well as natural deposits of precious stone or metal. They are also held responsible for volcanism.
In native Anglo-Saxon belief, dragons are always hoard-guardians. Interestingly, they often nest in barrows, i.e. burial-mounds, rather than in natural caves:
The dragon in Beowulf is attracted by gold and makes his home on a treasure hidden in a barrow—because that is how dragons roll. When a runaway slave steals a single goblet from the sleeping dragon's hoard, the dragon upon waking notices the theft and is so furious he breaks forth to devastate Geatland in revenge. In the earlier part of the poem, there is also a reference to another dragon hoard won by the dragonslayer Sigemund [sic] by killing a dragon in a cave.
The gnomic poem Maxims II contains the line: "a dragon must be in a barrow, oldnote or, depending on the translation, "wise" and proud of treasure"
Norse Mythology: The association of dragons with gold-hoarding was strong enough that "dragon's bed" (dreka beðr) is one of the numerous poetical paraphrases for "gold" in Old Norse poetry.
In the Saga Of Ragnar Lothbrok, princess Thora raises a tiny little baby dragon by letting it breed on a gold coin. The dragon grows to an alarming size, in the process hatching a massive pile of gold. One of the rare instances when a Hoarding Dragon is combined with a "save the princess" plot.
Book 2 of Gesta Danorum relates how young King Frode, looking desperately for money to pay his troops, hears about a giant venom-breathing snake that occupies a hill-like island on which much treasure is buried. Frode goes there, kills the dragon, digs up the treasure and thus regains his solvency.
A rather similar tale is told in book 6 of the same book about King Fridleif, who on a sea-journey is driven to an unknown island where a treasure is hidden in an underground chamber, guarded by a sea-dragon (who is then killed by Fridleif).
In East and South Slavic, especially Russian Mythology, dragons (zmeys) are shapeshifting creatures that can alternate between a reptilian and a human(oid) form. Accordingly they will not lie on hoards in a cave, but have palaces in far-away lands where they frequently own great riches. When zmeys demand tribute from humans, they will either demand maidens, or gold.
Dungeons & Dragons has the adventurers going up against a fire-breathing dragon and its hoard of gold coins.
In The BBC's Tolkien parody Hordes of the Things we are told that blue dragons hoard "those woolen foot-garments that men do call socks, stealing one only of every pair". So now you know where they went.
In Dungeons & Dragons, all dragons have hoards, typically three times as much treasure as other monsters of an equivalent power level. Beyond the sheer avaricious pleasure derived from wallowing in their coins like a pig, keeping a mental tabulation of their hoard's current worth, or maintaining an inventory down to the last copper piece, the Draconomicon explains that a dragon's hoard allows it to control the circumstances of its eventual demise. Rather than suddenly succumbing to the weight of centuries in its twilight years, a dragon may consume its hoard and choose to depart the earthly realm peacefully, or merge with the physical world and become a guardian spirit of one of its kind's nesting sites. Dragons also derive status from the size of their hoards, and bored wyrms may take up the (ludicrously complex) game of xorvintaal and compete for each others' treasure with the help of mortal "chess pieces."
The Draconomicon also provides examples of atypical dragon hoards. One eccentric bronze dragon maintains a collection of interesting driftwood and seashells from near her coastal home, a golden great wyrm has amassed an enormous library of rare books ("you can't learn anything from gold"), an unfortunate white dragon's hoard is held hostage by the tribe of ice giants enslaving him, while an enterprising blue dragon's greatest treasure is the salt mine he took over. It also features the Dragon Ascendant Prestige Class (limited to true dragons), which presents the concept that to a dragon of sufficient power and wealth (their hoard must be worth at least 100,000 gold pieces) consuming their entire hoard is enough of a sacrifice to start them on their way to divinity.
Even dragons with more traditional hoards may provide unique challenges. The sand dragons introduced in the Sandstorm supplement keep their treasures buried beneath the desert - hope your party packed a shovel alongside that 11-foot pole.
If a dragon is slain and its hoard looted, it may linger as a ghostly dragon, haunting the mortal plane until its stolen property (or treasure of an equivalent value) is returned to its sacked lair, after which it settles upon the loot one last time and disappears along with it.
The collective wealth and possessions of the dragon Dunkelzahn from Shadowrun basically constitute a hoard, and his comments indicate that dragons in general tend to accumulate them, whether they want to or not (it's described as a matter of collecting representations of their long memories and pasts). Dunkelzahn makes the idiosyncratic (and, among his fellows, controversial) decision to compose a will dividing and bequeathing his hoard in the event of his death (a large portion of which goes into funding an entire foundation dedicated solely to the execution of the will).
Lofwyr's hoard consists largely of Mega Corp. stock certificates, and as CEO and sole owner of Saeder-Krupp Heavy Industries he's the richest known entity on earth.
In the board game Dungeon Quest (original title: "Drakborgen"), the goal is to reach a dragon's hoard and steal as much as possible from it. But if you steal so much that you wake up the dragon, you die.
In Wagner's Ring of the Nibelung tetralogy (as adapted, with liberties, from Norse Mythology), the giant Fafner kills his hitherto-bro Fasolt for a hoard of gold (The Rhine-Gold) and is later found transformed into a dragon lying on the gold (The Valkyrie), until he is killed by Siegfried (Siegfried).
In the first game, there were three dragons. All of them had hoards, which you could try to loot (unwise, as the dragons typically noticed right away), or you could do a favor for each dragon and gain a reward.
In the aptly-named Hoard, you play as a dragon and get points for collecting treasure.
In RuneScape, many dragon lairs are littered with piles of gold. The extremely rare runite rocks are also usually found near dragons, because it is a delicacy to them.
In the game Blazing Dragons all the dragons eat gems which annoys the evil King George no end. However they're not fixated on them living lives just like a normal person.
The knight in The Cave has to fetch the gold from the dragon and give it to the princess in order to get her amulet to give to the king to pull the sword from the stone. Things don't go quite as planned....
In Discworld, Rincewind discovers a dragon's hoard. His joy for becoming a rich man is shortlived.
In Ancient Domains of Mystery, there's an underwater one guarded by a female water dragon. Trying to pick up an item there will make her warn you, and ignoring her will result in her trying to kill you.
The Red Dragon in Dragon's Crown is found in a room filled with all sorts of treasure. Said treasure room is very cramped, making fighting the dragon difficult.
In Dragon's Lair, the player's mission is to battle a dragon which also owns a hoard in a treasure room.
In Quest for Yrolg, you play as the imp servant of the evil necromancer Yrolg who has a dragon guarding his treasure room.
Dragon Age: Origins has a few dragons (most of them optional bosses) that have a lot of treasure to be plundered afterwards. Some of them are actually called "Dragon Hoard".
The dragon type Pokémon Gabite is noted in some of its Pokedex entries as habitually collecting jewels and storing them in its lair, though as with almost every entry, it's an Informed Attribute that's never actually seen in action.
Dragons in Dwarf Fortresstry to collect as much loot as possible during world generation, but in practice they only ended up with a handful of moderately valuable baubles. Everything in their lair will be worth less than random gear you get off one squad of bandits and isn't worth a tenth as much as the dragon itself, which drops up to 25 tonnes of flesh on death, all of which is worth 15 times as much as a normal animal's.
SCP Foundation: SCP-1779 are tiny reptiles which feed only on coins and make their nests out of them. They can grow to really big sizes, though...
In the French parodic literature series Kalon Le Barbare, it is stated that only male dragons build hoards, to attract females. It's only revealed after the "heroes" spent a whole chapter fighting a dragon that turned out to be female, and thus had no hoard of her own, much to their disappointment.
It's explained in My Little Pony: Friendship Is Magic that dragons are greedy by nature and will hoard things as an instinctive behavior. They also eat gems, which implies the heaps of jewels they keep around are actually their pantries. Specific episodes with dragon hoards:
In "Dragonshy", the mane six are sent on a diplomatic mission to a dragon who's taken up residence near Ponyville. Rarity speaks to the dragon and appeals his ego, a strategy that appears to work—until the dragon realizes she's helping herself to his treasure hoard, and he kicks her out.
"Owl's Well That Ends Well" features another full-grown dragon who gets angry and attacks baby dragon Spike for stealing from said dragon's hoard of gold and gems.
In "Secret of My Excess", it's revealed that hoarding behavior can cause dragons to undergo rapid growth, as a dragon's size increases with the size of its hoard. In the case of Spike, this leads to a nasty feedback loop, as this growth also decreases their mental faculties and makes them hoard more.
In "Dragon Quest", adolescent dragons are shown playing "King of the Hoard", a game which requires dragons to fight one another over a pile of treasure.