The Alleged Steed: d'Artagnan's yellow horse, which he disposes of as soon as he reaches Paris.
Which shows up again when Porthos is given an insult by his mistress.
In the 1921 silent film, d'Artagnan (Douglas Fairbanks) kisses the "embarrassing horse" goodbye after trading him for a new hat.
The Ace: Athos is essentially the perfect gentleman. His is born into high rank, has impeccable manners, a thorough education, and outstanding skill at arms. However, he also spends a lot of his life squandering his quality due to poor luck and a morose personality. He's also a pretty lousy hangman.
Arranged Marriage: Louis XIV's younger brother Philippe and Henrietta of England in Le Vicomte de Bragelonne.
Artistic License - History: Dumas was never a man to let the facts interfere with a good story. Particularly notable is that the entire first novel of the series is an anachronism: the name of D'Artagnan first appears in the records of the musketeers in 1633, five years after the novel ends and nearly a decade after Dumas's hero presents himself to M. de Treville. (Speaking of whom, the real Treville was himself a new musketeer in 1625, and wasn't made captain of the musketeers until, again, after the first novel ends.) Of the three musketeers after whom the novel is named, suffice it to say that they are entirely fictional creations with real names attached, and if they are ever historically accurate it is only by accident.
Badass Bookworm: Aramis, despite being a thorough womanizer and elite soldier, is also an academic with a passion for the clergy.
Badass Preacher: Aramis, once he rises through the ranks, eventually becoming Superior General of the Jesuits.
Bed Trick: d'Artagnan to Milady. She does not take it well when she finds out.
Begone Bribe: In Twenty Years After, Aramis relates an anecdote about a time when Cardinal Mazarin got into a disagreement with a prince whose alliance he desired:
... "The prince immediately sent fifty thousand livres to Mazarin, begging him never to write to him again, and offering twenty thousand livres in addition if he engaged never to speak to him again. What did Mazarin do?" "He took offense?" said Athos. "He beat the messenger?" said Porthos. "He took the money?" said d'Artagnan. "You have guessed right, d'Artagnan," said Aramis.
Bittersweet Ending: By the end of the first book, the titular heroes (plus d'Artagnan) win out against Milady and Richelieu, but at the cost of the death of Madame Bonacieux, d'Artagnan's love interest, not to mention how the trial of Milady has soiled the soldier's life for his three friends, leaving him alone within the Musketeers by book's end.
The first sequel, Twenty Years After, is just as bad. While they manage to end the Fronde civil war for now, and d'Artagnan gets promoted to Captain-Lieutenant of the Musketeers, the heroes fail to save Charles I, Athos kills what is hinted to be his son by Milady, Monsieur Bonacieux shows up, as if only to remind d'Artagnan of Madame Bonacieux, and d'Artagnan accidentally kills his friend Rochefort.
Blondes are Evil: Milady de Winter. Athos attempts to warn d'Artagnan against blonde women because they all remind him of his undead wife. It doesn't work.
Boisterous Bruiser: Porthos to some extent, and this trait is usually his primary characterization for all adaptations.
Book Dumb: d'Artagnan has no interest in academia, yet he's the group's idea man.
Bowdlerise: most adaptations of the book tend to portray D'Artagnan and the Musketeers as much more loveable than they are in the book, omitting such "small details" as their routinely seducing rich married women to fleece them out of their money, or making Constance into Bonacieux's daughter, rather than his wife, if not omitting Bonacieux entirely. In most adaptations, Athos merely banishes Milady from his lands (or, as in the 1993 Disney version, turns her in) instead of hanging her.
The Big Guy: Porthos, whose size and strength seems to grow with each book.
Does Not Know His Own Weight: Porthos once destroys a chair just by sitting in it. Made even funnier by his deadpan delivery of "Excuse me, but I need a new chair, I've broken this one".
Downer Ending: The final book, Le Vicomte de Bragelonne. Raoul loses his love interest to King Louis XIV, and heads off to war to die. When news of Raoul's death comes, Athos dies of sorrow. Aramis's scheme with the Man in the Iron Mask fails and he is forced into exile in Spain, and Porthos dies in the escape. d'Artagnan, after finally becoming the Marshal of France, is killed by cannon fire during a siege.
The Dragon: Rochefort, to Richelieu. Ironically, d'Artagnan becomes this to Mazarin.
Evil Chancellor: Richelieu, and Mazarin. While they both are quite loyal to France, having a King deciding things is quite unnecessary, thank you very much. This trait is overplayed to the hilt with Richelieu in adaptations that turn him into the main villain. In the books, Mazarin develops something of an unfair reputation as this trope due to his foreign nationality, although he also embezzles large amounts of money and gets away with it. In the final book, Colbert takes this position, compared to the most cavalier Finance Minister Nicholas Fouquet, and uses his financial influence to turn the king against Fouquet. Subverted in that it is Colbert's policies which subsequently make the country rich, militarily powerful, and capable of waging a foreign war in which D'Artagnan finally gets to be promoted to Field Marshal, while Fouquet - likeable as he was - had been embezzling the national wealth and spending it on grandiosely ornamental but ultimately useless architecture such as the chateau of Vaux-la-Vicomte or the fortifications of Belle-Isle, and it has to be said that he has richly (quite literally) earned his downfall.
Face-Heel Turn: Aramis in the final book (The Man in the Iron Mask), in which, not to be confused with the film, he alone (with Porthos tricked into it as dumb muscle) initiates the plot to replace the King with his long-imprisoned twin brother - which is actually foiled with D'Artagnan's assistance, although Fouquet takes the major credit and thus postpones his downfall by a few days. The point being that it turns out the kingdom is best served by having the original Louis as king, Colbert as finance minister, and D'Artagnan in charge of the army, than it ever would have been served by his brother who, knowing nothing about the state of affairs but what Aramis told him, would have had to rely completely on Aramis and leave the likeable but corrupt Fouquet to embezzle and squander what was left of the treasury, and that D'Artagnan's loyalty to Louis ends up being the right choice, and Aramis's plot therefore makes him a traitor and a true Face Heel Turn since he betrays not only his King but also the whole Musketeers group by an act that he knew neither D'Artagnan nor Athos could be persuaded into, and Porthos only by trickery. And the irony being that Fouquet plays a major role in saving Louis even though he knows Louis is working for his downfall, and it was in his interest to cooperate with the substitution: and Louis's first act after being saved is to dispose of Fouquet in favour of Colbert.
Part of the point of the book is that some of the older generation (like Athos) believe that a nobleman's duty is to serve the king no matter what. Aramis' actions violate this principle (and he manipulates Porthos into doing the same); d'Artagnan isn't sure what to think about this but ultimately lands on the side of the King.
Femme Fatale: Milady, one of literature's great villainesses. To much lesser extent, also Madame de Chevreuse.
Fire-Forged Friends: When d'Artagan first meets up with the three musketeers, in sequence, he ends up having to face a duel with each. It's when the Cardinal's men try to arrest them and they fight them off that the four of them become friends.
Averted in the later books. Athos spends most of an entire book helping Charles's son retake the English throne, D'Artagnan does as well, but for the Money, Dear Boy.
Forgotten Phlebotinum: In the first chapter, d'Artagnan has a secret recipe for a balm involving oil, wine, and rosemary, which can heal any wound, no matter how grievous, in the space of a day or two. By the end of chapter 27, his musketeer friends have each been wounded — Athos more than once — and at no point does d'Artagnan think of using this balm to bring them back to health.
Funetik Aksent: Used in the original French and some translations, with d'Artagnan's Gascon accent coming out when he exclaims, "Mordioux!" The Swiss soldiers also talk funny. ("La graisse te l'oie, il est très ponne avec des gonfitures."/"Goose grease is kood with basdry.")
Genre Shift: A large portion of Louise de La Vallière is taken up with court intrigue and romantic plots, with the titular musketeers explicitly absent from the narrative. They don't make a real return until Man in the Iron Mask where the series returns to it's original adventure tone.
Historical-Domain Character: Louis XIII, his wife Anne of Austria, his minister Cardinal Richelieu; Louis XIV, his mistress Louise de La Vallière, his ministers Cardinal Mazarin and Jean-Baptiste Colbert; the English monarch Charles The First of The House of Stuart, his wife Henrietta Marie, his Parliamentary opponent Oliver Cromwell; and even The Man In The Iron Mask, who was an actual person, though very little is known of him. (That's of why he has been such a popular figure in fiction.)
Historical Villain Upgrade: In the books, Richelieu is an adversary of the Musketeers, but not an actual villain. In many adaptations, though, he's turned into the Big Bad. The same goes for Mazarin and Colbert.
Averted with Oliver Cromwell. While he's definitely an antagonist, he is nothing compared to the outright villain Mordaunt.
I Have Many Names: Milady. Also the titular Three Musketeers, as they all use aliases, and later take up new titles.
Intergenerational Friendship: At the beginning of the story, D'Artagnan is 19 and Athos is said to be twice his age. The age gap is explicitly noted in-universe, as well as the father/mentor role played by Athos.
Interrupted Suicide: d'Artagnan in the later book, believe it or not. And the person who stops him? Louis XIV.
It's All Junk: The much-passed around sapphire ring, at least to the original owner.
Jail Bake: Used in Twenty Years After to free the Duke of Beaufort.
Jumped at the Call: d'Artagnan leaves home as soon as he is an adult to find his fortune with his sword arm.
Raoul as well. In the second book, as soon as he is sent off by Athos, he jumps into the Fronde civil war, although his youth leads him to make a few bad calls.
Karma Houdini: Richelieu, despite opposing the Musketeers through most of the first book, winds up just as powerful as he was when the book started. He can even give d'Artagnan a promotion. And in the second book, Athos even wishes he were alive again instead of Mazarin. This is presumably as the real Richelieu stayed in favor with the king. In adaptations that make him into the Big Bad, however, he is usually defeated.
Lawful Stupid: Nicolas Fouquet in the third novel, although it may be a case of Honor Before Reason (since he saves King Louis from the plot to replace him, knowing that this will mean his own downfall as Louis and Colbert work against him.) Also, Athos in the later books displays some elements of that and Honor Before Reason.
Lost Him in a Card Game: Athos very nearly does this to Grimaud in a dice game after losing two horses and quite a lot of other stuff. D'Artagnan is not amused to find his diamond ring playing a prominent role in the story.
Lost in Translation: The most well-known English translation renders the French écu as "crown", because most British readers at the time the translation was made would be familiar with how much a crown was worth. (A modern British reader would probably think of £0.25, thus throwing off the sense of how much an écu was actually worth.)
Luke, I Am Your Father: Athos is really the father of his ward Raoul, but he never tells him, disclosing the information only to Raoul's mother (who is also Aramis' former mistress).
Magnetic Hero: Athos in Twenty years after. He and Aramis go to England to help King Charles I while d'Artagnan and Porthos (acting on Mazarin's orders) are supposed to be on Oliver Cromwell's side. It takes Athos one scene to convince d'Artagnan that a true gentleman can only fight on the king's side.
Mark of Shame: Milady's Fleur-de-lis brand marks her as a criminal.
Master Swordsman: more like a whole Master Swordsmanship Academy (the Musketeers, with special mention for four main characters). Raoul, Jussac and Rochefort also qualify.
Protectorate: In Twenty years after, D'Artagnan protects young King Louis from an angry mob.
Retired Badass Roundup: In Twenty years after, D'Artagnan tries to reunite his old friends on the orders of Cardinal Mazarino. Porthos, now a wealthy widower, accepts but Athos, who regained his title and estate as the Comte de la Fère and Aramis, now a priest, refuse. Athos and Aramis are members of the Fronde, the anti-Mazarin rebellion. After a few chapters, they are kicking ass together again.
Roaring Rampageof Revenge: Mordaunt in the second book. He kills his uncle for disinheriting him, and acts as the executioner for Charles I for the same reason. He also kills the executioner of Lille for murdering Milady (while posing as a monk and denying him absolution!). He then spends the rest of the book trying to kill the Musketeers.
Shoot the Dangerous Minion: Richelieu is happy for this reason when the heroes kill Milady and gives D'Artagnan a promotion/job as a reward. While the Cardinal was willing to use her services, he's Affably Evil, whereas she was a psycho vamp and thus he was happy to be rid of her.
Silly Reason for War: The Duke of Buckingham was willing to go to war with France if diplomatic relations broke down... because it would keep him away from the Queen of France that he was in love with.
Slave Brand: Milady de Winter has a brand marking her as a convicted criminal.
Sword Fight: Despite being Musketeers, the heroes usually favor their swords. This changes somewhat when we see them on the battlefield. This is justified though by the weapons technology of the time which required a lengthy reloading process between shots (but they have their servants for that).
Tailor-Made Prison: In Twenty years after, D'Artagnan and Porthos have been captured on the orders of Cardinal Mazarin and are imprisoned in Rueil Castle. Mazarin requests thirty extra soldiers to guard exclusively the two "special guests". Unsurprisingly, they manage to escape anyway.
Tampering with Food and Drink: D'Artagnan receives a case of wine along with a note that indicates it's from his fellow musketeers. Before he can drink any of it, an enemy mook drinks some and dies...it was poisoned wine sent by Milady to kill him.
10-Minute Retirement: D'Artagnan in The Vicomte de Bragelonne, twice. The first time to help reinstate Charles II of England, the second time because King Louis has imprisoned Athos in the Bastille.
Took a Level in Badass: EVERYONE in the sequel Twenty Years After, as a result of Character Development. Athos is wiser, Porthos is stronger, Aramis is far more cunning, and d'Artagnan has gone from naive to a brilliant strategist. Two of their servants also take a level. Porthos and Aramis's respective servants, however, do not.
Although it's obvious that Mous(que)ton, Porthos's servant, has more adventuring experience than the much younger Blaisois.
Time Bomb: the Queen's diamonds must be brought back from England in time for that ball!
Tired of Running: At the beginning of Twenty years after, Porthos and D'Artagnan are assigned the task of recapturing the Duke of Beaufort who escaped from the Bastille. After a long chase, the Duke decides to stop and fight back.
Trojan Prisoner: In "Twenty years after", Athos and Aramis are taken prisoners by Porthos and D'Artagnan.
Very Loosely Based on a True Story: Dumas's novel is based on Courtilz's novel, which is very loosely based on a true story. D'Artagnan was a real man, and even some of the fictional characters are based on real people — or at least their names.
Vow of Celibacy: Two examples of villains who don't respect their vows of celibacy:
Richelieu, being a cardinal and all, is supposed to be celibate. However, he's revealed to have made unsuccessful advances to the queen, a fact used both to illustrate his character and to add to his motivations (since he's bitter at being rebuffed).
Milady de Winter is a Femme Fatale who started out as a nun. Her first seduction was of the priest of her convent, whom she convinced to run away with her (and with the convent's sacred chalice).
You Killed My Mother: Mordaunt. Our heroes try to explain what a murderous bitch Milady was, but Mordaunt makes it clear he just doesn't care.
Warrior Prince: le Grand Condé, a member of the Royal family and an outstanding military commander. His victory at Lens is depicted in Twenty years after
What the Hell, Hero?: Athos and d'Artagnan give one or two to Louis XIV due to his romancing Raoul's fiancée.
Wicked Cultured: The Cardinal just like his Real Life counterpart is an outstanding politician and diplomat, hardened veteran, poet and playwright.
Wild Mass Guessing: According to TheOtherWiki, going back as far as the 1950s, it has been considered that Milady's Fleur-de-lis was actually meant as a symbol that she was a hermaphrodite, (the idea being that the criminal nature of the Fleur-de-lis alone isn't enough to justify the extreme revulsion it induces in those that discover it) and was inspired by the historical figure the Chevalier d'Éon. (This information has since been removed from The Other Wiki.)
Woman Scorned: A male example; we learn, fairly late on into the story, that one of the reasons Richelieu is determined to bring down the Queen is because she rejected his love. (Highly unlikely in Real Life, as we have it well on record that Richelieu disliked Anne as much as she did him.)
Adaptations and spin-offs with their own pages include:
Eyepatch of Power: In La Fille de d'Artagnan worn by Athos, although he occasionally switches it from right to left and back because he has two good eyes.
Flynning: In every film and stage adaptation, except (and in stark contrast averted) in the 1973 series.
Race Lift: One of the mascots for the candy bar (see below) is black.
Someone to Remember Her by: In La Fille de d'Artagnan d'Artagnan (Philippe Noiret) is moved almost to tears when he first lays eyes on his now grown-up daughter because she resembles her dead mother Constance so much.