The Acts of Caine: Berne to Caine. To summarize a lengthy spiel, while both are vicious and skilled fighters, Berne is The Hedonist, while Caine has a cold discipline.
Roland's outward confidence contrasts with Terra's constant internal self doubt. He is also well liked, but ultimately cynical as opposed to Terra who is disliked by others, but ultimately idealistic. Roland's very nature as a liar clashes with Terra's brutal honesty. A big contrast is Roland's innate skill and mastery of the shieldwatch and aeon edged sword, both of which Terra struggles to master through nothing more than hard work.
Hikari is beautiful, skilled, and praised by others, but seems to have suffered from a traumatic past that makes her distance herself from close relationships. Terra's looks are average at best, she has no combat skills at all, and is actively ignored by others, but had a stable home life that provides her with emotional stability.
Delphia is gorgeous and always entering new romantic relationships. Terra is ordinary in appearance and has never experienced a romantic relationship. Delphia is indirect and breaks down into tears with even the slightest hint of a confrontation. Terra is blunt, thrives on confrontation, and never cries.
Kairos was also Alya's squire, just like Terra, but Kairos had an excess of talent and a strong connection with fate unlike Terra who struggled with every aspect of the academy and has no connection with fate at all.
In Animorphs, it's all over the goddamn place. All the main characters act as foils to each other to some extent.
Marco is foil to Jake (taking orders vs. giving orders), Tobias (pragmatism vs. idealism), Cassie (pragmatism vs. moral relativism) and Rachel (subtlety vs. brute force).
Jake is foil to Marco (taking orders vs. giving orders), Rachel (leadership vs. insubordination; they say this is what happens when two "strong" personalities mix), Tobias (confidence vs. insecurity) and Ax (leadership vs. loyalty to authority figures).
Cassie is foil to Marco (pragmatism vs. moral relativism) and Rachel (peace vs. conflict).
Tobias is foil to Rachel (peace vs. conflict), Jake (confidence vs. insecurity), and Marco (pragmatism vs. honor).
Rachel is foil to Marco (subtlety vs. brute force), Jake (leadership vs. insubordination), Cassie (peace vs. conflict), Tobias (peace vs. conflict) and Ax (giving orders vs. taking orders).
Ax is foil to Jake (giving orders vs. taking orders), Marco (pragmatism vs. "warrior ethics"), and Rachel (emotion vs. logic).
Ellimist and Crayak act as foils to each other (life vs. death, the forces of good vs. the forces of evil). Even their original mortal forms contrast this way (a blue, sky-dwelling, feathered alien vs. a red-eyed, subterranean, muscular alien).
Visser Three is foil to Visser One (psychopathic, sadistic, irrational evil vs. pragmatic, intelligent, everyday evil).
Visser Three is a foil to Alloran. Visser Three declared his brother a traitor and was responsible for him being forced into hiding, whereas Alloran's brother was the one with the goal of killing Alloran.
The Yeerks' two main Slave Mook races are foils to each other. The Hork-Bajir are arboreal herbivores who lived peaceful lives until the Yeerks took them by force, while the Taxxons are subterranean carnivores who hate their Horror Hunger so much that they allied with the Yeerks out of desperation.
Bazil Broketail: Alsebia is one to Purple-Green. He is a brute who relies on strength and ferocity in battle, while she is a Master Swordsman who prefers subtlety over direct approach. He is a wild dragon who is never quite civilized while she is the most intelligent and human-like of her kin, even refusing to eat horses which she finds beautiful but which Purple-Green (like most dragons) considers just a tasty delicacy. She even outright calls him a "stupid savage" once when annoyed by his rather ill-thought idea.
The first, and most direct example is a contrast between Holden's roommate and next-door neighbor at the start of the novel. He begins to describe his roommate Ward Stradlater as the type of handsome that parents notice, while pointing out that Robert Ackley has crumby hygiene and an acne problem. As the story unfolds, though, Ackley is more socially awkward than nasty, while Holden also remembers Stradlater's insistent (to the potentially date-rapey point) actions toward the girls he dates. After starting a fistfight with Stradlater (after realizing that he might have done something sketchy to a girl Holden cares for this time), Holden takes refuge with Ackley and shows that he's likely just a decent average kid with some self-esteem issues.
Holden constantly brings up this girl, Jane Gallagher, to the point where she seems like she is a potential romantic interest. She's "muckle-mouthed" and other people (such as Holden's mother) don't think she's attractive, but she is the only one who he feels comfortable talking to about his brother's death. In contrast, the one date he goes on during the novel is with Sally Hayes — a wealthy, pretty, popular girl who is everything Holden claims to despise. Even though the characters never meet (since he never even speaks to Jane during the few days that the book covers), Jane's supposed sensitivity and Sally's near-stepford obliviousness contrast in how Holden speaks of each of them.
The first few chapters deal with Holden failing out of his third Prep School. Mr. Spencer, his history teacher and a kind old man, wants to talk to him about his failing grade, but only seems to alienate Holden. Toward the end, Holden visits another teacher from his past, Mr. Antolini, who is described as younger and more understanding. Unfortunately, Holden wakes to Antolini (ambiguously) touching him in his sleep, and leaves hastily out of self-protection.
Touma Kamijou was born with the power in his right hand, Imagine Breaker, the power to change things back to normal, sees saving and helping people as something anyone would do, and is oblivious to all the girls in love with him. Kakeru Kamisato was an Ordinary High-School Student who one day gained a power in his right hand, World Rejecter, the power to create new worlds to tempt and trap people in (specifically stated to be Imagine Breaker's opposite), sees his power and role as a hero to be a burden, and notices he has an Unwanted Harem and hates having one. Kakeru comes into conflict with Touma when Touma doesn't agree with his views on their powers. Kakeru believed Touma didn't like having powers and tried to get him to join him on his quest to get revenge on the beings he believed responsible for granting them.
Accelerator and Shizuri Mugino have powers that concentrate on destruction while Teitoku Kakine has powers that concentrate on creation. This aspect of their rivalry is actually lampshaded.
Mikoto Misaka and Misaki Shokuhou. Both are Level 5 espers who go to the same prestigious school and are around the same age. Mikoto is good friends with a few people and is a relatively normal and well-adjusted person, while Misaki has an enormous clique (whom she frequently mind-controls) and is extremely paranoid and never trusts anyone. Their powers are starkly different: Mikoto's ability to control electricity is very versatile and makes her especially effective against machines, whereas Misaki's ability to control the human brain is much more limited (including being useless against machines). It's also eventually revealed that they're both in love with Touma, because he saved both of their lives (in separate incidents). However, while Touma and Mikoto interact fairly regularly, Misaki tends to stay out of his life because he can never remember her.
Misaki Shokuhou and Seria Kumokawa. Both are experts in controlling human minds, but Misaki uses her esper ability while Seria manages it entirely through normal techniques. Misaki works for generally selfish reasons, while Seria works for the good of Academy City (by advising one of its directors). And, as with Mikoto and Misaki, they're both in love with Touma.
Motoharu Tsuchimikado and Fran Karasuma. Both are spies sent by the Anglican Church to infiltrate another faction: Academy City for Motoharu and the Kamisato Faction for Fran. Both are knowledgeable about both science and magic. However, while Motoharu became a Wild Card who passes information to both sides, Fran came to genuinely love Kakeru, though she eventually leaves his group of her own will.
Chillin' in Another World with Level 2 Cheat Powers: The brothers Gholl and Yuigarde are quite different. The former is a thoughtful leader while the latter is brash. The former cares about the lives of his soldiers to the point of willing to avoid taking victory if he thinks the cost in demon lives isn't worth it while the latter thinks nothing about sending them to their deaths to achieve victory at any cost even when it's clear it isn't working.
But not all men seek rest and peace; some are born with the spirit of the storm in their blood, restless harbingers of violence and bloodshed, knowing no other path. . . .
Opal is the human daughter of the dragon Yong. They spend most of their time yelling at each other, and she completely fails to realize that it's because they are Too Much Alike. The most obvious is how they are both extremely stubborn and refuse to back down for any reason, but they also both love treasure, especially art and history, and hate accepting help from anyone. Opal also has a number of subtle draconic traits, such as growling and snarling when she gets angry. She's especially annoyed when her mother notes that her little collection of the valuables she's found is basically a dragon's hoard.
On the other hand, Opal's mother is perfect in absolutely every way except for the fact that she's not a mage. She is the World's Most Beautiful Woman, a true genius, loyal to a slavish degree, and runs Yong's entire empire by herself for no reason than that she wants to make his life easier. She's the exact opposite of her daughter, who is a failure at everything. And then when her dragon is in danger she flies a squad of attack helicopters into enemy territory while having no idea where she actually needs to go. Opal has spent the last three books doing basically the same thing, minus the military hardware.
Sybil: Wow. I see where you get your recklessness from now.
The earliest example is Rincewind and Twoflower, who react to danger in completely opposite manners.
Granny Weatherwax and Nanny Ogg. Both are powerful, smart, and tough-as-nails Lancre witches. But Nanny is easy going, has a huge family, behaves in a friendly manner, and is usually drunk and telling bawdy jokes. Granny is serious, stoic, never married, feared and respected by all, and has no sense of humor. Naturally they are best friends (and argue a lot).
Vimes and Carrot. Vimes is a cynical, grouchy, dirty-fighting former drunk who has no respect for authority (especially kings). Carrot is an optimistic, ultra-friendly, honorable young officer who always obeys the letter of the law (and may secretly be a king). To make it more complex, Vimes is also clearly a true idealist deep down (his cynicism results from how disappointed he is at the world), while Carrot can show remarkable cunning and deviousness for someone so innocent seeming.
Lord Vetinari and Leonard of Quirm: they're both extremely intelligent, but Leonard is a naive Ditzy Genius who's fascinated with everything, trusts everyone, and doesn't have very good social skills, and Vetinari is uninterested in anything too scientific or technical, trusts almost no one, and can manipulate people into doing just about whatever he wants. There's a bit of a mirror-image quality to their conversations: Vetinari explains whatever devious schemes are on his mind at Leonard without expecting Leonard to understand because he really just wants to talk to himself to get his thoughts in order, and Leonard assumes Vetinari understands all the odd scientific things he's up to even though obscure scientific knowledge isn't exactly Vetinari's forte.
Eric and Four in Divergent. The former preaches all-out combat with no mercy rules, while the latter preaches fair fights with protective rules.
The Empirium Trilogy: Corien is a foil for the Prophet. They both used to be angels who were forced into the Deep by the Saints. Both use their angelic powers in order to achieve their goals and they both became leaders of powerful organizations. That's where the similarities end: unlike Corien- who hates humans and can't forgive them for what the Saints did- the Prophet has nothing but love and understanding for humans. As such, she's naturally on the opposing side, and tries to help out where she can, both with Rielle during the Second Age and Eliana in the Third.
The Epic of Gilgamesh makes this trope Older Than Dirt. Gilgamesh is hot-headed and arrogant, and uses his status as god-king to always get his way, (especially with the young brides) so in response to the people's prayers expressing annoyance with Gilgamesh, the gods create Enkidu, a wild beast-man who is tamed via The Oldest Profession and becomes the only person who can rival Gilgamesh's strength, thus holding him accountable for his actions. Whereas Gilgamesh is bold, arrogant, and hasty, Enkidu is level-headed and expresses understandable fear at the things Gilgamesh wants to do.
The most obvious are Lady Tamarind and Beamabeth Marlebourne, who are beautiful, graceful and charming rich young women of very high social standing, respected and beloved by everybody. Mosca, on the other hand, is a dirt-poor, "ferret-faced" daughter of an exiled historian, despised and shunned by most. Lady Tamarind turns out to be a religious fundamentalist, which is the furthest thing from Mosca, while Beamabeth is simply an Alpha Bitch with no regard for anyone but herself — Mosca, on the other hand, really does believe in something greater than herself, in spite of her cynicism.
There is also a subtler, but interesting dynamic with Mosca and Aramai Goshawk: both have animal themed names, except Mosca's animal is a fly, which is typically seen as a less "noble" animal than, well, a goshawk, neither has a permanent residence. Mosca has a lot of stereotypically male, unladylike attributes (rage-prone, abrasive, loud-mouthed, swears a lot) and wears breeches under her skirt, Goshawk has some feminine attributes, like little delicate white hands and a chatelaine, normally worn by housewives. The colour associated with Mosca is black (the black of her hair and eyes, a fly motif), the colour most associated with Goshawk is, oddly enough, white, even though he does wear all black (the white of his hands, his face and his eyes). Mosca is centered on the accumulation of spiritual wealth - words and books, Goshawk is centered on the accumulation of material wealth. Both set up elaborate schemes, but through completely different means, for completely different ends and from completely different positions.
Ayn Rand loves these, as her characters are archetypes more than they are people. In The Fountainhead, Roark is The Hero and all the others are those who could have been the hero, except for one minor moral failing, or deliberately choosing to be evil, soulmoney-sucking leeches, etc. At least for the men. Women get this treatment, too.
Hans's family can be considered as the polar opposites of Agnarr and Idunn. While Agnarr and Idunn love their children and each other, Hans's father picks favorites among his 13 sons while letting them torment each other out of contempt and cruelty, and is at best apathetic towards his wife. Also, while both are responsible for children developing mental health issues, Agnarr only wanted to keep his daughters safe, but Hans's father is unfeeling towards his sons.
On another note, the Southern Isles is the complete opposite of Arendelle. While Arendelle is a democratic monarchy whose royal family is open and friendly towards their subjects, the Southern Isles is a totalitarian Police State whose regime brutally crushes any dissent while squeezing its people via high taxes.
Sibling relations. While the two sisters got along with and wanted to reconcile with each other, the 13 brothers do not get along with each other, as their father deliberately encouraged violence within his large family. Hans's thoughts throughout the book indicate that he even planned to rub his achievements in his brothers' faces. The brothers are also willing to use dubious means to achieve their father's respect.
In Galaxy of Fear the siblings Tash and Zak Arranda gradually differentiate more, with Zak being Book Dumb while Tash is a Bookworm, Zak being more impulsive and physical, and so on. The two Shi'ido scientists, Hoole and Gog, also contrast; Hoole shape-shifts often and takes combat forms but mostly remains in his default form, Gog never fights but is constantly taking forms for The Infiltration to the point where his default form is rarely seen. Hoole also is The Atoner, while Gog... not so much.
In Gautrek's Saga, King Gautrek is not very bright but very generous; his friend Jarl Neri is clever but a pathological miser.
Good Omens: As a duo, Shadwell and Madame Tracy are a foil for Aziraphale and Crowley: two people who initially appear very different, but who after a many years working in close proximity realize they're not so different after all.
It was the sort of sensible arrangement that many isolated agents, working in awkward conditions a long way from their superiors, reach with their opposite number when they realize that they have more in common with their immediate opponents than their remote allies.
In Catching Fire, the reaction of Katniss's family and friends is neatly contrasted with that of her prep team, of whom Katniss observes that they never had to be strong for anyone else. (The District vs. the Capital, in small-scale.)
Later in Mockingjay District 13 acts as one to the Capitol. The Capitol is dependent on the districts, while District 13 is self reliant. The Capitol's people live in luxury, while the people of District 13 have only there basics needs. In the end it is revealed that Alma Coin the leader of District 13 is just as tyrannical as President Snow, the leader of the Capitol, without his redeeming honesty.
Blair Bissel in Divided in Death is this for Roarke, in that he is not brave, not particularly smart, is greedy, has no conscience, has a fragile ego, and has conquests rather than relationships, unlike Roarke. Eve puts a lampshade on that.
Magdalana in Innocent in Death is this for Eve, in that she is rich, a thief, loves no one but herself, is charming, speaks French and Italian fluently, and will use Roarke to achieve her ends, unlike Eve. Eve makes a comment about Magdalana being the "anti-me".
The Irregular at Magic High School characters Tatsuya and Kichijouji are similar, except that they serve different clans. Both are socially awkward Badass Bookworms who're eternally loyal to their aristocratic School Idol patrons. Rivalry was instant.
The invertebrates to James's aunts in James and the Giant Peach. Both are adoptive parents of James. However, while James's aunts are closely related to James and treat him like a slave, the invertebrates are each of a completely different biological phylum to James and genuinely love him.
Also from Le Mis, Grantaire acts as as foil to Enjolras. Enjolras is a serious man who cares for no one but his revolution, Grantaire is a drunkard and is only in the revolution for Enjolras and cares not for the actual revolution.
The Machineries of Empire: Kel Cheris and Shuos Jedao. Cheris is a straightforward Kel who's a math prodigy to the point where everyone's surprised she's not a Nirai (of the scientist caste). She's an infantry captain and her signifier, the Ashhawk Sheathed Wings, means she's very stable mentally. By contrast, Jedao is a cunning Shuos, has dyscalculia, has mostly led fleets throughout his career and his signifier, Immolation Fox, is considered an alarm bell by people who know the meaning of it.
In the Malazan Book of the Fallen, Clip serves as a foil to Nimander Golit. Where Nimander is humble, conflicted and secretly badass, Clip is boisterous and self-confident despite having only a fraction of Nimander's skill. They are set in direct contrast to one another where the leadership of their group is concerned. Clip shows up and seemingly usurps Nimander's position in the group, but it is later revealed that the other Tiste Andii only put up with Clip because Nimander does.
Max And The Midknights: Conrad the Kind and his brother Gastley. Conrad is the Good King of Byjovia who cares deeply about his people, while Gastley is a Jerkass who only cares about being on top. Under Conrad's rule, the people of Byjovia are all friendly, while under Gastley they all become Jerkassesthanks to Gastley's guards spiking the town's water supply with a potion made from Conrad's blood. Conrad is a very large, friendly guy, while Gastley is Lean and Mean.
Isabelle Lightwood is the seasoned, snobbish, girly Nephilim to Clary Fray's naïve idealist tomboy.
Sebastian/Jonathan Morgenstern to Jace: He was experimented on with demon's blood while Jace was experimented on with angel's blood. Valentine raised him to be cold, cruel, and sadistic, while Jace is more compassionate and kind.
Aline Penhallow to Isabelle Lightwood; she's conservative and shy where Isabelle is outspoken and outgoing.
In Mr. Standfast, the supporting character Launcelot Wake acts as a foil to the main villain, Otto von Schwabing. The protagonist initially likes and trusts von Schwabing('s cover identity) and despises Wake, but comes to realise that he's wrong about each of them. Von Schwabing approves of the War and has encouraged it for his own ends, but (although a bold man in his own world of espionage) loses his nerve when he gets caught in the field of actual battle. Wake is a committed pacifist on idealistic grounds, but no coward, and shows great courage when he starts working in the war zone first as a Red Cross worker and then as a messenger. At the climax of the novel, their deaths occur in quick succession and are directly contrasted, with Wake being fatally wounded while carrying a vital message under heavy fire and von Schwabing getting himself killed by cracking up and running out in front of his own side's guns.
Stolz to Oblomov. The latter is a lazy and pessimistic Cloudcuckoolander; the former is industrious and optimistic.
Played for Drama in A Prayer for Owen Meany. The titular character, while physically weaker than the narrator, is self-driven, determined, assertive, and has a good head on his shoulders, if not a bit bullheaded. In stark contrast, Johnny is passive, unmotivated, socially off, maladjusted and after Owen's death, utterly lost and stuck in a rut.
Quantum Gravity: The worlds serve as this. Interestingly enough, all of them are foils for all the other ones:
Demons of Demonia are very focused on knowing and being yourself, regardless of what that is, in contrast to the different social rules in all the other realms.
The Fair Folk of Faery, for instance, deliberately hide things from themselves and forget. They are also the strongest aetherically, throwing them that much farther from Otopia.
Elves in Alfheim are masters at hiding themselves, throwing them away from the demons; and also at self-control, in contrast with the generally more playful fey. Their system of alliances would also make anyone from another realm dizzy, and their True Names are very powerful.
Zoomenon is everything broken down into its pure state, meaning the creatures/beings there do not always have what we would call a consciousness, and it is a much harsher environment than anything you'd be likely to find in the other realms outside a volcano or something similar.
The titular characters are a demon and angel respectively, whose physical appearances (he wears black spiked armor and had black demonic wings to contrast with her white dress and wings and personalities (he is stoic, quiet, and snarky and she is kind, spontaneous, and cheerful) differed. The places they live in reflected this as well: Juliet's is a peaceful, well-lit, and beautiful realm as opposed to Romeo's gloomy, perilous, and quite frightening one. Despite the current war between the two races, this doesn't stop them from falling in love.
The whole political and interplanetary conflict is embodied in the characters Frank Chalmers and John Boone. Frank is an unlikable cynic who believes that people are stupid and afraid to make hard choices, forcing people like him to seize control for their own good, and works with Mega Corps to try and minimize their depredations. John is a charismatic idealist who thinks Mars colonization is an opportunity to distill the best qualities of Earth societies and ceate something new and worthwhile, and opposes interference by the Mega Corps as an intrusion of old, stifling systems.
The philosophy of terraforming is argued mainly by Sax, a proponent who wants to turn the planet green, and Ann, who thinks it should be preserved in a pristine state. (They both have Meaningful Names: Saxifrage is a plant known for breaking apart rocks, and Ann's surname is Clayborne.)
Sadako and the Thousand Paper Cranes has Sadako Sasaki and her friend Kenji, both of whom have leukemia. While Sadako is optimistic and has a close support system from friends and family, Kenji has given up on getting well and gets few visitors apart from Sadako.
The vikings and blood brothers Hjalmar and Odd in The Saga of Arrow-Odd. Hjalmar became a viking so he will be able to marry princess Ingibjorg back in Sweden, and voluntarily adheres to a chivalrous code of honor. Odd is quite ruthless, fights for his fame only, is not attached to women and plans never to return home.
Louise Glück's poem "Saints" contrasts the lives of Glück's grandmother and aunt, her family's titular "saints": while the former was "cautious and conservative" and lived a quiet life, the latter was more spiritual and rebellious, and thus suffered more.
The Secret Garden: Colin to Mary — both spoiled brats who gradually begin to redeem themselves, Mary faster than Colin. It is through him that the beginnings of her growth are emphasized and encouraged. In fact, to begin with, he's practically her Shadow Archetype.
Sherlock Holmes and Doctor Watson are classic foils. Holmes leaps into plans without explanation and follows up on wild clues. Watson, as his namesake trope points out, tends to ask realistic questions and accept more conventional theories. Holmes is also highly excitable when "the game is afoot" and Watson, a war veteran, is a skilled marksman and cool-headed in combat.
This extends to physical attributes. The two times Watson is described physically, he is "thin as a lathe and brown as a nut" in the first book, and "strongly built, with a square jaw and a thick neck", several years later. This description (plus the mustache) acts as a physical foil next to Holmes's thinness, pallor, and severe, aquiline features. He's also usually portrayed as having brown or blond hair, while Holmes's is black.
The Devil’s Dust by James Lovegrove sees Holmes and Watson join forces with Allan Quatermain and Umslopogaas in investigating a plague in an African mining town that led to the death of Quatermain’s son Henry, who was acting as a doctor in the town when the plague broke out. Throughout the narrative, Watson in particular observes the contrast between Holmes and Quatermain, reflecting that Quatermain is a man of action and the past where Holmes represents the man of intellect and the future, although the two men still respect each other despite their contrasting methods of finding information.
The Stormlight Archive: Szeth to Kaladin. Both value honor and despise the actual act of killing, and are both slaves after a fashion. In the debate of To Be Lawful or Good, Kaladin falls under "Good", while Szeth ascribes to a version of "Lawful", matched, unsurprisingly by the types of Radiant they become. Whereas Kaladin takesresponsibility foreverything, Szeth takes it fornothing. The powers they exhibit are also similar. However, Szeth is an assassin, not a soldier, and is not actually a surgebinder until joining the Skybreakers, who are rivals to the Windrunners, which Kaladin is one of.
Every character in The Stranger is basically a foil for the narrator, Meursault. Not surprising, of course, since the point of the novel is to develop a particular Existentialist philosophy.
Temeraire: Captain Rankin, to the protagonist Captain Laurence. Each is a cultured Officer and a Gentleman of noble birth in the British Aerial Corps, and Rankin is briefly Laurence's first friend there. However, where Laurence is kind-hearted, respects the Corps dragons as people, and does his duty even at great personal cost, Rankin turns out to be a Bitch in Sheep's Clothing who abuses and neglects his (fully sapient) dragon and only cares about his own advancement. One reader noted that Rankin habitually refers to Catherine Harcourt as 'Miss' because that is what properly-socialized gentlemen do, whereas Laurence makes a point not to when first corrected because Harcourt clearly prefers to be called 'Captain' and he can imagine no reason for a properly-socialized gentleman to give offence by not obliging her.
In Those That Wake, Mike is one to Mal. Mike is an older man who can't fight for anything because he believes he's worth nothing, while Mal is a young man who fights no matter what because fighting is the only thing that gives him purpose.
In the sequel, Aaron and Rose are foils to Laura. Aaron is a child genius who believes in the good that technology can bring, while Laura is a teenager who doesn't believe technology is good. Rose is clingy and fragile, while Laura is stronger and assertive.
The Hobbit: Smaug and Thorin. They're both Kings under the Mountain according to themselves - Smaug is The Usurper to Thorin's Rightful King Returns. Thorin and Smaug have the same Fatal Flaws of Pride, and Greed (for the same freaking treasure no less), and both their goals and motivations are pretty self-centred. They also both blockade themselves and their treasure inside the same mountain and wish for others to leave them alone with it or otherwise face Disproportionate Retribution. Furthermore, both take a more active role in the plot in the present time frame for Revenge. Both of them expect others to treat them like nobility, but Thorin is definitely more tolerant of not getting this than Smaug is, whilst Smaug has a lot more charm when he's talking to others than Thorin does. Smaug is a formidable One-Man Army and is seemingly alone in the world, whereas Thorin operates with (and often relies on) other dwarves and Bilbo Baggins. Smaug is huge whereas Thorin is a dwarf. Smaug is a Genius Bruiser whereas Thorin makes some bad decisions on his own. Smaug is red and gold, while Thorin wears blue and silver colors. Thorin commands the loyalty of the other Company dwarves to the point his nephews die defending him and he makes a Heel–Face Turn out of his Sanity Slippage; Smaug has no such redeeming qualities.
Boromir to his brother Faramir as well as to Aragorn, as while he had similar heroic goals, he is a Tragic Hero who is tempted by the Ring.
Saruman and Gandalf are both powerful wizards, however, Saruman is seduced by power, whereas Gandalf refuses to take the Ring. In The Two Towers, Gandalf says that he is Saruman as he should have been.
Denethor and Théoden are both the rulers of their countries who succumb to the influence of Sauron and Saruman respectively (Denethor via the Palantír, and Théoden through the influence of Wormtongue.) Both kings also struggle with despair, having lost their son. Ultimately, Denethor succumbs to despair and commits suicide, but Théoden triumphs over it and dies an honorable death in battle.
Denethor and Faramir: both are noble and powerful pure-blooded Númenóreans with the abilities to read the hearts of other men and to command over them, who share a love for ancient lore and other scholarly pursuits over feats of arm. Yet all these similarities only highlight their differences: the son is warm, gentle and understanding where the father is cold, harsh and scornful. Faramir chooses to keep on fighting despite having lost all hope, Denethor succumbs to despair. Faramir demonstrates humility and open-mindedness, Denethor displays arrogance and stubbornness, etc...
The Silmarillion and The Children of Húrin: Tuor and Túrin. They're cousins (though they almost never meet), both their fathers are lost in Nirnaeth Arnoediad, they are separated from their human families to be fostered by Elves, go live in hidden Elven cities, fall in love with Elven ladies... However, Túrin is a rash, not always sympathetic Tragic HeroBlessed with Suck while Tuor is an all out good guy who ends pretty well — what with being one of the few characters who actually survive to the end of the book.
The ValarAule and Melkor/Morgoth. They are both Valar who have their own ideas and don't always work with Eru's plans for Arda. However while Aule tried making his own life, creating the Dwarves, he repented of doing so when Eru reprimanded him and Eru gave the Dwarves true life for this. In contrast Melkor 'creates' his own creatures by corrupting Eru's creations, such as the Orcs being made from corrupted Elves. Aule created Dwarves out of a desire to populate the Earth and actually loves his creations as his children. Melkor breaks with Eru's plans out of envy and doesn't love his creations, Tolkien wrote Morgoth would have eventually destroyed them.
Eärendil and Maglor. Both are grandsons of High Kings of Noldor. Eärendil is the genetic father of Elrond and Elros; and he, albeit of son of mortal Tuor, sets sails to West to seek help of Valar to beat Morgoth. Whilst away, the Sons of Fëanor attack Sirion, and whilst Eärendil's wife Elwing escapes with Silmaril, she leaves young Elrond and Elros basically orphaned. Maglor then becomes their foster father. With Silmaril, Eärendil and Elwing eventually arrive to Valinor, and Eärendil chooses the life of Elf (although his heart was more on his father's kindred). He eventually becomes the Lightbearer, sailing forever the vastness of the skies with Silmaril on the mast of his ship, and becomes the sign of hope to Elves and Men. Maglor, on the other hand, eventually gets his hand on the Silmarils, find them burning him because of his (and his brothers') foul deeds, defies the consultation of the archangels of Arda, casts his Silmaril into sea, and is doomed to wander forever the shores of Middle-Earth, singing of pain and regret, never returning amongst the Elven nations, and never even being granted the relief of death like Men. He is presumably still around somewhere...
Alanna and Kel, the first two female knights in a hundred years. Alanna actively hid and shunned her femininity for years; Kel was proud of her position as the Girl. Alanna is hot-headed and short tempered; Kel is reserved and stoic. Alanna is prone to resenting authority, while Kel is obsessed with duty. Alanna is the prototypical lone hero, while Kell is an effective commander and leader.
George and Jonathon also served as foils to on another, in something resembling Betty and Veronica. Both were natural leaders with devious natures, but George was much more practical and down-to-earth, while Jon was more haughty and big-picture oriented.
Sarai and Dove from the Trickster Duet. Both absolutely hate the treatment of the Raka, but they respond to it in different ways; Sarai rages and rants against it, while the more quiet and sensitive Dove speaks to the people. Eventually Sarai runs away, leading to Dove taking her place as future Queen.
In the Twilight series, there is Bella and Leah. Both are completely and utterly in love with someone (Edward and Sam respectively) and both suffer devastating heartbreak when he leaves them. Bella reacts by going into a Heroic BSoD until Edward returns, abandoning plans of any future or attempts at emotional healing. Leah is forced to move on, fighting to protect Forks and, by Breaking Dawn, planning to deal with her anger issues via yoga and going to a nearby community college. Interestingly, Bella is the hero in this situation, while Leah is meant to be disagreed with.
Lux Arcadia and his older brother Fugil. Both are princes to the Old Arcadia Empire, but Lux is the seventh prince (hence last in the line of succession) whereas Fugil is the first prince. Lux is an idealistic hero who tries to save everyone, a concept which Fugil dismisses as foolish and naive. Or rather, that's how Fugil presents himself. It is heavily implied that Fugil is much closer to Lux in personality than is initially apparent.
Lizsharte "Lisha" Atismata and Listelka Rei Arshalia. Both are first princesses of the New Kingdom Atismata and the Holy Arcadia Empirenote This is different from the aforementioned Old Arcadia Empire, respectively. Lisha is inexperienced with politics, isn't afraid to get her hands dirty on the battlefield or as a mechanic of Drag-Rides, and wants to do the best for her people. In contrast, Listelka is a skillful manipulator, doesn't do any fighting personally, and looks down on the common folk. Both of them are in love with the Arcadian princes mentioned above, but in different ways. Lisha and Lux have a relationship of equals and trust each other, while Listelka thinks that Fugil is her loyal and submissive knight when it's obvious to everyone else that he's manipulating her.
Lux and Yoruka Kirihime. Both are royals of fallen countries, but Lux played a pivotal role in overthrowing his while Yoruka worked for the country that destroyed hers (in a failed attempt to prevent it from doing so). Both lacked any rights to the throne, Lux because of being the youngest son and Yoruka because of being a born killer. Both are top-level Drag-Knights, but Lux fights while trying to spare his opponents while Yoruka is an assassin specialised in killing techniques.
Rosa and Hayes both became Ax-Crazy psychos in order to cope with feelings of powerlessness and inferiority. Both were saved by someone (King of Vices for Rosa, Listelka for Hayes) who wanted to use them as disposable pawns while promising them glory. Both went through varying degrees of brainwashing, with Rosa being heavily brainwashed while Hayes received light suggestion and had her personality intact. Finally, Rosa pulls a Heel–Face Turn after realizing her master's ideology was just cowardly escapism while Hayes dies unrepentant of her elitist and sadistic lifestyle.
In the battle between the Seven Dragon Paladins and the seven Ragnarok, several of the opposing pairs are foils in terms of powers. Lux (who avoids the enemy's attack and adapts his behaviour to counter them) fights Yggdrasil (which receives the enemy's attack, regenerates and adapts its body to resist further attacks of that kind), Greifer (who can become invincible for brief periods) fights Metatron (which reflects all attacks, except during brief periods of vulnerability), Mel (who can raise and lower temperature) fights Fenrir (which can only lower temperature through its freezing breath), Magialca (who pilots the powerful but immobile Jormungandr) fights Phoenix (who is the most mobile Ragnarok due to flight), and Rosa (who controls many Drag-Rides that are expendable due to being unmanned) fights Poseidon (which has numerous tentacles that are expendable since it can rapidly regenerate them).
In the Unicorns of Balinor series, Ari and Chase (her bonded unicorn) are foils. Chase is a proud, Hot-Blooded warrior who believes he should go out and fight allthe Shifter's minions, right now. Ari is a insecure, cautious girl who often reminds him that they can't serve the rebellion if they get killed. This relationship makes them highly effective on solo missions- even though it sometimes results in mid-battle arguments.
In Vampire Academy, the dhampirs Janine Hathaway and Olena Belikova stand as foils, representing the different life choices presented to dhampir women. Janine chose her career as a guardian over romance and family life. She travels the world with the Moroi family she is sworn to protect. Olena chose to settle down early and devoted herself to raising a family. She has never set foot out her hometown of Baia.
In Victoria, Nazi model officer Captain Halsing is this to the protagonist, Marine captain John Rumford. They share a common military background, as well as a philosophical and idealistic temperament, but whereas Rumford is a staunch believer in Christianity, democracy and the American Way, Halsing is equally devoted to Nietzschean philosophy and technocratic Nazism. Also, unlike Rumford, he is well-polished and polite. For Rumford, it is eerie to meet an enemy who is so much like himself, in some ways arguably better than himself, and yet the very embodiment of his own ideological antithesis.
In James Swallow's Warhammer 40,000Blood Angels novels Deus Encarmine and Deus Sanguinius, Sachiel is used as a foil to Rafen, for his Pride. At his first appearance, Rafen remembers their rivalry and how Sachiel had always preferred to talk, and Rafen to let his actions speak for themselves. Most starkly contrast when Sachiel thinks Rafen dead (No One Could Survive That!!) and gloats to the empty air — "Rafen, you are dead." — versus when Rafen sees Sachiel's corpse and feels sorry for him.
Oz to Dorothy in The Wonderful Wizard of Oz. Both are people from the civilized world who were transported to the Land of Oz and mistaken for great magicians. However, while the plot of the book revolves around Dorothy trying to return to the civilized world, Oz stayed in the Land of Oz and let the people of the land think he was there most powerful wizard.
