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.
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.
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).
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 unwavering determination to return his people to their homeland is nothing short of admirable.
Lightning Bruiser: He's a lot faster and more agile than you'd expect a dwarf to be, and doesn't seem to have sacrificed any strength for it.
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.
Royals Who Actually Do Something: Taking back Erebor is no easy task, but Thorin firmly believes that it is his responsibility as the dwarven king to reclaim his people's homeland. And 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..
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.
"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."
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 affect 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.
He also recognizes the smell of dwarves on Bilbo, so he knows that Bilbo was in the company of dwarves. He also made sure to have gems and gold covering his soft underbelly, negating his one weakness. Pity he missed a spot.
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.
Lovecraft Lite: Since 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 even less like demigods and more like semi-sentient beasts.
Talking Animal: Justified by the fact that they're the offspring of the half-spider demigoddess known as Shelob, who was in turn the child of the demonic entity known as Ungoliant. However, Bilbo is only able to understand them because he is wearing the ring.
The Master of Lake-town
People of Lake-town: He may have a good head for business, especially his own business, but he is no good when anything serious happens!
Adipose Rex: Notably not the "Rex" part officially, but as ruler of Lake-town, he's still the head honcho.
Corrupt Bureaucrat: Even when he is helping the heroes he is ultimately after his own selfish interests.