A Hobbit chosen by the wizard Gandalf to accompany 13 dwarves on a quest to reclaim the Lonely Mountain and its treasure from the dragon Smaug.See The Lord of the Rings character sheet for tropes that apply to him in that work.
British Stuffiness: Bilbo is very much modelled on a country squire of Tolkien's era or slightly before: shackled by manners and a code of propriety from expressing himself (even when facing a home invasion by thirteen uninvited guests). Through the story, Bilbo slowly loses those inhibitions via his exposure to the forthright dwarves and learns to speak his mind but tempered with the tact and subtlety of his upbringing. In his conversation with Smaug he's able to amuse the dragon with his riddling speak and yet land a number of solid blows against Smaug's overpowering ego with the surgically precise application of blunt linguistic force.
Character Development: At first he's more or less useless. Starting when he picks up the Ring, he becomes a lot more brave and competent. By the time he gets the dwarves out of the Elven-king's dungeon, he's the de facto leader.
The Chosen Zero: Gandalf is the only one who has faith in him in the beginning; the dwarves and Bilbo himself think he's unfit for the journey.
Gentleman Adventurer: By the end of the book he's quite embraced his adventurer persona. This also has the effect of ruining his good name in Hobbiton.
Gentleman Thief: Lampshaded. When he's offended, the dwarves assume that he's the kind who prefers to be called "expert treasure-hunter" or the like.
Guile Hero: Unlike his dwarven companions, Bilbo prefers to use his words and brain to get him out of tight situations. His tiny size and dislike of battle also makes this trope necessary to his survival throughout the quest.
Hard Head: Knocked unconscious twice without serious consequence.
The Load: Until he saves the dwarves from the spiders. After that point, he's pretty much carrying the team.
My God, What Have I Done?: When Bilbo locates and pockets the Arkenstone, he knows what it is, what it means to Thorin, and that it was almost certainly meant to be excluded from the "pick your own share" clause of his contract. He nicks it anyway, admitting that "Now I truly am a burglar". It's only later that he tries to make good of his action by handing it over to Bard and Thranduil to use as a bargaining chip with Thorin (which in itself is a pretty dodgy action but done for the purest motives).
Cool Sword: Orcrist, an elven sword. Although it's confiscated by the Wood-elves and never returned while he is alive; he later uses a dwarven axe from the Lonely Mountain's armories.
Dark and Troubled Past: Poor Thorin's had a pretty rough life. His kingdom was taken over by a dragon that either killed most of the Erebor dwarves in the initial attack or forced them to flee to distant lands; much of his life afterwards was spent working in menial, dead-end jobs that brought little respect from the humans around him. Very shortly after his grandfather was brutally murdered by Azog for daring to set foot inside the gate of Moria; the Longbeards' original strongold and Thorin had to fight in a war of vengeance against the orcs climaxing in the Battle of Azanulbizar which cost his people a huge percentage of their fighting strength (essentially every dwarven male of fighting age fought in the battle) including his brother. Not long after that his father embarked on an attempt to take back the Mountain on which after several years of getting nowhere he disappeared, presumed dead, and Thorin spent the next hundred years burdened with the fact he'd have to do likewise or be a failure of a king, 'an heir, but an heir without hope'. Very little seems to ever go right or come easy to the poor guy.
Determinator: Despite his many flaws, Thorin's determined to reclaim his clan's rightful ancestral homeland and treasure.
Deuteragonist: Thorin is the second character after Bilbo, because the quest is to restore Thorin as King under the Mountain.
Disappeared Dad: His father, Thráin, disappeared attempting to reclaim the Mountain when Thorin was ninety-five, leaving Thorin to care for and guide the exiled dwarves of Erebor alone.
Enemy Mine: Thorin is forced to team up with the Elves and the people of Lake-Town after learning that the Goblins and Wargs are marching to their location. Ironically, this is what prevents Thorin from becoming a Fallen Hero.
Et Tu, Brute?: Has this reaction after Bilbo betrays him by giving the Arkenstone to Bard and the Elves to use as a bargaining chip.
Greed: His quest has an undercurrent of this, since it's not just to take Revenge on the dragon and reclaim his ancestral realm but also to reclaim its hoard of treasure, despite not exactly living in poverty anymore - though he does have a valid claim to it, more than the invading dragon who drove his people out. Comes to the fore when the lingering "dragon-sickness" effect of the treasure affects his judgment, increasing his gold-lust.
Odd Name Out: The only dwarf with a last name, and the only one whose name doesn't rhyme with or otherwise sound similar to that of at least one other dwarf in the company. Though it does rhyme with his great-great-uncle Borin (great-grandfather of Balin, Dwalin, Óin, and Glóin).
Old Soldier: At One hundred and ninety-five one of the oldest out there, and a veteran of the Goblin Wars.
Parental Substitute: To his nephews, Fíli and Kíli. And to Bilbo in a soft son, disapproving dad kind of way (whereas Balin is more of a cuddly uncle figure).
The Patriarch: The dwarves are fiercely patriarchal, considering themselves all descended from the original seven 'Fathers' of the dwarves. Thorin, as king of the eldest clan (the Longbeards or Durin's Folk) is the symbolic father of the entire race. In The Hobbit, he displays all the qualities of a more literal patriarch among his company, including the tragically late expression of his respect for the black sheep, Bilbo.
Rightful King Returns: The goal of his quest, apart from killing Smaug, is to restore himself to Erebor's throne.
Royals Who Actually Do Something: Taking back Erebor is no easy task, but Thorin firmly believes that it is his responsibility as the king of the Longbeard dwarves to reclaim their ancestral home and riches. And (as revealed in later books) despite his sometimes arrogant behavior, Thorin is also willing to do the same work and menial jobs as his fellow dwarves in exile.
Screw Politeness, I'm a Senior!: Thorin specifically does not introduce himself to Bilbo by declaring to be "at your service", nor does he assist the other dwarves in doing the washing-up after they eat, and throughout the rest of the book his manners are rather brusque and business-like. This could also be a case of "screw politeness, I'm important" as well.
Cool Old Guy: Balin, while not especially old for a dwarf, looks the part and is one of the closest to Bilbo.
Color-Coded Characters: Tolkien lists the colors of the Dwarves hooded cloaks, as if that would help you keep them straight. If you pair up colors and names in the orders they are both listed, you should get:
Dwalin - Dark green
Balin - Scarlet red
Fíli and Kíli - Blue
Dori and Nori - Purple
Ori - Grey
Óin - Brown
Glóin - White
Bifur and Bofur - Yellow
Bombur - Pale green
Thorin - Sky-blue with a long silver tassle
Conservation of Competence: Generally limited to Thorin, and later Bilbo. See: the only ones not immediately jumped by trolls, the only one who keeps his bow out in a forest, the only one with a plan to escape Mirkwood... the others may or may not get a moment before the major battle. Balin too is depicted as having good judgement.
Disappeared Dad: Balin and Dwalin's father Fundin fell at Azanulbizar and so became one of the Burned Dwarves- the casualties of the battle were too numerous to be buried according to dwarven custom.
Old Soldier: Like Thorin, both Balin and Glóin are veterans of Azanulbizar. Dwalin and Óin were also probably there since they're both older than Glóin, but they're not confirmed as being there by Tolkien (incidentally, Glóin was a mere sixteen at the time, half the age of a dwarf considered 'Battle ready'- Azanulbizar must have been a desperate battle indeed).
Balin. He's the first dwarf to take Bilbo seriously and later is the only one to stand up for him when he falls out with the other dwarves.
Dori is often the last person to escape a tough situation, and also often the one to risk himself to help out Bilbo.
Sibling Team: Fíli and Kíli; Balin and Dwalin; Óin and Glóin; Nori, Dori and Ori; and Bofur and Bombur (plus their cousin Bifur). note Nori, Dori, and Ori are never actually mentioned to be siblings, but can obviously be assumed as such..
"A very good tale! The best I have heard for a long while. If all beggars could tell such a good one, they might find me kinder."
Anti-Hero: He's a very dangerous individual and Gandalf warns that meeting him at night, while he's in bear form, would be a bad idea. He's also not fond of dwarves—but he also hates goblins more, and will help if talked around in the right way.
Scheherezade Gambit: Gandalf gets the Company into his house in a two-part gambit. Beorn would have turned them away if they'd all shown up at once, but when they come two at a time while Gandalf tells the story of their adventures, he has to let them all in out of sheer exasperated curiosity.
Shape Shifter: Known as a "skin-changer" in-universe, Beorn can assume the form of a giant black bear.
Greed: Sets out to claim the treasure of Smaug, with no intention to share it with others - like, Thorin and the dwarves or the men of Laketown.
Hero Antagonist: He's unequivocally on the side of good, what with fighting in the Last Alliance against Sauron and siding with Thorin and Bard against the goblins, but he's also arrogant, greedy, and bigoted toward dwarves, and stands firmly in the way of their quest. He learns his lesson by the end, though.
Royals Who Actually Do Something: Initially set out to capture the treasures of Erebor for himself, but turned around to help the people of Laketown when he learned about the disaster that struck them.
Shell-Shocked Veteran: Became this after witnessing his father and most of his folk die during the Battle of the Last Alliance.
Bard the Bowman
"The dragon is coming or I am a fool!"
The captain of Lake-town's archers, he is actually of the lost noble house of Dale.
Asskicking Equals Authority: He is acclaimed king by many in Lake-town because he kills Smaug and he leads the contingent of Men in the Battle of Five Armies because of this also. But since Smaug had just destroyed Lake-town he still submitted to Lake-town's Master until it was finally rebuilt.
Badass Normal: Even the dwarves are said to use spells (albeit to ward treasure rather than any battle magic). Bard is an ordinary foot soldier with no special powers.
Chekhov's Gunman: First appears unnamed, musing about the dwarves' arrival. He is later named and described in more detail.
Good Is Not Soft: Everyone knows him as a cranky bastard; after Smaug, he joins the people camping outside Erebor hoping for some Dwarf treasure. But he's also a fair and just man.
Hyper Competent Sidekick: Towards the Master of Lake-Town. When the latter flees during Smaug's assualt on the town, Bard Holds The Line and ultimate kills Smaug. It reaches the point where the town wants to dispose of the Master and make Bard their new leader.
Improbable Aiming Skills: Kills Smaug with one shot, through a tiny hole in in the armour of gems that had embedded into the dragon's soft underbelly over decades.
Last Stand: Died at the same day the siege of Minas Tirith entered its final phase, defending the corpse of King Brand of Dale.
Hero of Another Story: There has to be an interesting backstory behind the ruler of the Iron Hills, right? His backstory includes numerous battles there against Easterlings, he fought at Moria, and he eventually died in battle during the War of the Ring.
"Lake-men, some nasty scheme of those miserable tub-trading Lake-men or I'm a lizard. I haven't been down that way for an age and an age; but I will soon alter that!"
A dragon in the Third Age, Smaug is the last great dragon left in Middle-Earth, and the main antagonist in the Hobbit. Prior to the events in the story, he lay waste to Dale and captured Erebor, the Lonely Mountain, from the Dwarves. For two hundred years he hoarded Erebor's treasures.
Affably Evil: Being erudite, Smaug appreciates good conversation.
You have nice manners for a thief and a liar.
Badass: He's an ancient, powerful dragon, it comes with the territory (see Our Dragons Are Different). He also single-handedly destroyed a kingdom, killing nearly all of its people, and captured a city.
Badass Boast: Biblo tries to make a comment that he and the company came for revenge on Smaug for everyone he's killed, he responds with a VERY lengthy one that's practically descends into a speech on how awesome he is.
Revenge! Revenge! The King under the Mountain is dead and where are his kin that dare seek revenge? Girion Lord of Dale is dead, and I have eaten his people like a wolf among sheep, and where are his sons' sons that dare approach me? I kill where I wish and none dare resist. I laid low the warriors of old and their like is not in the world today. Then I was but young and tender. Now I am old and strong, strong, strong, Thief in the Shadows! My armor is like tenfold shields. My teeth are like swords. My claws, spears. The shock of my tail, a thunderbolt. My wings, a hurricane. And my breath, death!
Composite Character: Tolkien designed him as based on the two iconic dragons of the Norse lore (which he considered "the only true dragons"), Fafnir and the dragon that Beowulf killed. The former is the basis of his witty, sassy personality, while the later is the reason he flies, breathes fire, and is nigh invulnerable.
Dangerously Genre Savvy: "The Quest of Erebor" in Unfinished Tales, Gandalf states that part of the reason he pushed Bilbo into joining Thorin and Co. on their expedition was because Smaug knows the scent of dwarves too well for them to effect a stealth mission, but the dragon would likely not be familiar with the smell of a hobbit. Smaug, in his ultimate moment of Genre Savvy, bypasses this discrepancy of knowledge by tracing the origin of Bilbo and the dwarves to Lake-town and attacking there instead.
His rage passes description - the sort of rage that is only seen when rich folk that have more than they can enjoy suddenly lose something that they have long had but never before used or wanted. His fire belched forth, the hall smoked, he shook the mountain...
To hunt the whole mountain till he had caught the thief and had torn and trampled him was his one thought.
He would not forget or forgive the theft, not if a thousand years turned him to smouldering stone, but he could afford to wait.
The Dreaded: No one even went near him for decades after he claimed Erebor. The Dwarfs, even Throin, are too afraid to enter the Mountain when they know he's there. It's stated that many of the people defending Lake-Town would've just fled from Smaug without a fight when he attacked, if not for Bard's orders and constant encouragement.
Evil Is Petty: A mild taunt or taking ANYTHING from him, no matter how insignificant, is enough to provoke him to violence.
Evil Laugh: In the book, his laughter is enough to floor Bilbo and shake the mountain.
Famous Last Words: The last sentence of dialogue he has in the book (not counting his thoughts when he's attacking Lake-Town). Even these are a badass boast.
Smaug: They shall see me and remember who is the real King under the Mountain!
Hannibal Lecture: In a sense his entire conversation with Bilbo is this, but in particular when he spreads doubt in Bilbo's mind about the dwarves and how (or whether) they actually intend to pay him his fourteenth share- there being nothing in the agreement about providing transport or guards for his journey home, and it would take longer than he has to live to even steal it all.
The homonym with "smog" was probably deliberate as well.
'Smug' is also a very appropriate homonym.
Non-Malicious Monster: The strangest thing about Smaug? You probably could survive an encounter with him. If you appeal to his vanity and constantly praise him of course.
Our Dragons Are Different: They talk for one. The animated version has a head more resembling a ravening wolf than a giant lizard. The animated and live-action movies go for a saurian appearance as well, while Tolkien actually made a painting of Smaug himself and depicted him as more narrow and serpentine (Smaug is called a "worm"; the Old English form wyrm connoted both "snake" and "dragon".)
Pooled Funds: Smaug just loves to wallow in gold. He has a lot of it, considering he can burrow in and be completely covered, despite his vast size. Invoked Trope of Money Fetish; it's his, even though he doesn't spend it.
Pride: And appealing to it is the only thing that saves Bilbo.
Red Baron: Aside from "the Golden" above, Bilbo reels off a whole list of titles for Smaug at one point. The most common is "the Magnificent".
Revenge: The Battle of Five Armies is caused in part by the Misty Mountain goblins wanting to avenge him, along with all the spoils for the taking. They stir up other clans of goblins and they all converge on the Lonely Mountain.
You Killed My Father: He has a grudge against the dwarves due to the death of his father, Azog, at Dáin's hands.
"If beggars will not wait at the door, but sneak in to try thieving, that is what we do to them. If any of your people poke their foul beards in here again, they will fare the same. Go and tell them so! But if his family wish to know who is now king here, the name is written on his face. I wrote it! I killed him! I am the master!"
Karmic Death: He started a war with the dwarves after beheading Thrór, where he was himself beheaded. Also, he taunted Thrór's companion by throwing a bag of coins at him. Years later, the dwarves put Azog's own head on a pike and stuffed that same bag into his mouth.
Lovecraft Lite: A fraction of their ancestry is demonic in nature, due to being the children of Shelob, and thus the grandchildren of Ungoliant. However, the demonic traits they inherited from their mother and grandmother are not as prominent (apart from the abilities to speak and produce webs of darkness), making them less like demigods and more like semi-sentient beasts.
Sleazy Politician: When the people of Lake-town berate him for fleeing the scene too soon when Smaug attacks, he successfully shifts the blame on the dwarves for rousing the dragon in the first place (and he's not half wrong either).