Nightfall Series: Initially, Tristan seems to be a vain Pretty Boy, whose only redeeming quality is his Undying Loyalty to the Big Bad. Later on, his Back Story reveals that as a human he was a reclusive poet, fighting to find his place in the world. After he becomes a vampire, he develops a great capacity to care for others and struggles with his inability to create art.
In the final story arc of Animorphs, Jake relinquishes command for a short period. When he becomes leader again, he's an absolute authority figure, and refuses to second-guess himself or let anyone else question his decisions, working from the standpoint that "a leader who shows weakness invites disaster". This ultimately leads him to becoming the most ruthless character in the series.
Bridge of Birds has Miser Shen, a seemingly comical character who lives up to his name by hoarding wealth. It's only when he loses said wealth do we find out his backstory. Shen's village was razed because he was unable to pay the duke's taxes. His daughter died in the purge and Shen was so devastated he look for a way to bring her back. He discovered that there was a giant who could grant his wish by paying him heavily. Shen then spends the rest of his life making money until he completely forgets about his goal.sob
Sherlock Holmes himself: e.g. in "Three Garridebs", he shows a vulnerable side that despite the usual veneer of an exacting, calculating mind does care for Watson very deeply. And despite his famous initial claims in "Study in Scarlet" that he only remembers things he needs which the solar system and other topics like that aren't, he for example often quotes classic literature and probably knows much more about history than strictly necessary for his profession (a typical example being him calling Watson his Boswell). He also later expressly admits to having a bit of an artistic mind as well, and is known to enjoy and actively seek out good music.
Late in King Kelson's Bride, Sofiana reveals to her Camberian Council colleagues her previous role as godmother and arcane tutor to Mátyás Furstán. She implies that they intentionally downplayed his arcane abilities: "He was also a formidable pupil of the ars magica even then—far more formidable than I felt his brothers should know." She goes on to say that he came to her secretly for help when he learned of his brothers' plans, and that she and Azim (another Councillor) covertly assisted him.
Severus Snape, on the surface a Sadist Teacherand later apparently revealed to be The Mole, turns out to be a Double Agent and the The Atoner who is torn over his feelings towards the son of the man he hated and the woman he loved, both of whom he involuntarily got killed (hence the atoning).
Fleur Delacour at first appears to be a highly vain woman who only cares about Bill because of his looks. She later surprises everyone when it is revealed that she genuinely loves her fiancé after a werewolf attack leaves him with some very ugly scars—she views them as badges of honor.
According to Pottermore, Minerva McGonagall fell in love with a Muggle after graduating from Hogwarts. He proposed, and she accepted, but then turned him down because she knew he wouldn't go with her to London where she would be working for the Ministry.
In Dan Abnett's Gaunt's Ghosts novel First & Only, Dorden, The Medic, improvises an explanation for a wounded Naval man that not only shifts the blame from them but puts it on their opponents. When the troopers with him comment, he reveals he had been an amateur actor.
In Traitor General, Mkvenner reveals that he knows Old Gothic. Better than Gaunt does, even.
In Honour Guard, although Hark has been assigned to the Ghosts to bring down Gaunt, he capably assists Gaunt's mission, even after Gaunt decides to defy orders (although he does try to arrest him immediately, until it is clearly impracticable.
In another Warhammer 40 000 book, Black Legion, Telemachon Lyras is at first considered to be little more than one of hedonistic, sensation-seeking, Slaanesh-worshiping psychopaths of the Emperor's Children. However, it's revealed he does seek a purpose beyond hedonism and is, most prominently, the first character to get the Anamnesis to show human emotions by giving a surprisingly heartfelt account of Chemos's legends.
In The Bell at Sealey Head, Miranda Beryl arrives at the house of her dying relative and seems a perfect city-loving Blue Blood. Then, when Emma see Ridley Dow caught in magic and is unable to rescue him, Miranda calls him by his first name, which works, and arranges for him to be brought to a room with total competence and complete disregard for what happens to her clothes in the process — and evinces knowledge about magic. Whereupon she recruits Emma to help her keep up the facade of a Blue Blood heiress waiting for her inheritance.
In The Riddle Master Trilogy, several characters have hidden depths, including Morgon, the peaceful farmer-Prince of a remote island, who is the last one anyone (including himself) expects to get caught up in prophecies that will affect all the lands; Raederle, who has inherited more than she knows or wants to know from the mysterious shapeshifters beneath the sea; and the pig-woman of An who Raederle befriends.
The Truth - Mr. Tulip of the New Firm is a mountain of dumb muscle with a bizarre Verbal Tic and a habit of snorting anything in powdered form, including icing sugar and crushed mothballs; he's almost too stupid to be really malicious, except that he really is great at killing people. He does, however, turn out to have a --ingphenomenal appreciation for art history, capable of pointing out to various curators the provenance, quality and legitimacy of a wide range of pieces, and sometimes weeping over their splendour. All while hulking there with his ill-fitting suit and bloodshot eyes, dribbling drain cleaner and saying "—ing" every sentence.
His backstory is only hinted at throughout the book. In many ways, he's one of Pratchett's most interesting characters because we're shown that the little we know has an explanation, but that the explanation itself is mostly hidden. It's tragic to see him struggle with traumatic childhood memories while casually murdering people. To quote the book itself, "Sometimes Mr. Pin heard him wake up screaming in the middle of the night."
Vimes also seems to have a lot more to him than Noble BigotCowboy Cop. But in his own words "He knew he had hidden depths. There was nothing in them he wanted brought to the surface".
Carrot, while initially innocent and naive, later develops this in spades. He's so good at it that even career con-man Moist von Lipwig can't read him.
All three of the witches are fairly obvious character types: Granny is The Determinator — a mean, strong, unyielding powerhouse, whose main flaw is that she can't admit she's wrong; Magrat is an overly-romantic wet hen who gets steamrollered by Granny; and Nanny's a disgusting old baggage whose main role seems to be as Plucky Comic Relief. But later books reveal Granny is full of self-doubt and not lacking a form of kindness; right from the beginning it's clear that Magrat has a core of iron; and Word of God is that Nanny is more powerful than Granny, but cultivates an image that hides this because she has less will to use it. Being a witch seems to require having Hidden Depths; they're where the Second (or Third) Thoughts come from.
Some trolls get this in low temperature environments, especially Detritus. In their first appearance it is revealed that the oldest trolls will sink so far into philosophical questions that they are essentially dead unless somebody wakes them up by, say, starting a fire in their mouth.
History Monk Lu-Tze has some pretty deep hidden depths.
Jane Austen's Pride and Prejudice is all about Hidden Depths, with the main character learning that first impressions are not the only barometer of a person's character (the dashing charmer turns out to be a scoundrel, the uptight dullard is revealed to be a decent, honourable and caring man, etc). There's a reason Jane Austen initially called it First Impressions.
Raptor Red - Red's sister is, for most of the story, a manic, easily-angered character who is deeply suspicious of almost every creature that isn't her sister. Imagine Raptor Red's surprise when she finds her playing slide-down-the-snow-hill with a pack of Troodon. "Sister - playful. The concepts do not go together."
Gandalf: Hobbits really are amazing creatures, as I have said before. You can learn all that there is to know about their ways in a month, yet after a hundred years they can still surprise you in a pinch.
In Jim Butcher's The Dresden Files novel Death Masks, Michael reveals that his wife Charity made his armor. In Proven Guilty you find out she also spars with Michael, has her own armor, and was a dark magic witch who was sacrificed to a dragon (which is how she met Michael). In the same book Charity and Harry storm the heart of the Winter court Artic Tor to rescue Molly.
There is also "Cujo" Hendricks, "Gentleman" Johnny Marcone's bodyguard and top enforcer. A typical linebacker who communicates in grunts, totes machine-guns one-handed and generally looks like the Dumb Muscle. Hendricks is shown to be deeply committed to his boss' safety, as well as madly in love with Sigrun Gard, one of his co-workers. Even later he is stated to have studied Philosophy on a football scholarship before one of his knees gave out, and is shown working on his Master's degree in his spare time. He also quotes Chaucer at his boss when the boss does something he doesn't like.
In the Dragonlance novels, the elven princess Laurana is initially regarded as little more than a Brainless Beauty, but when challenged she proves to be a brave warrior, skilled diplomat and inspirational leader whose innovative tactics lead her army to a series of remarkable victories in the Vingaard Campaign.
You know Raistlin, right? The gloomy, pessimistic, bitter, snarky, mage in sour armor? Turns out he's quite the entertainer, having started performing as a street illusionist at a very young age, to feed himself and his brother. Kids love his shows!
In A Song of Ice and Fire, every character has Hidden Depths. However, with some characters, the surface is removed and you find out that underneath, they're worse.
In Suzanne Collins's Catching Fire, at the end, Katniss learns she's the Unwitting Pawn. Who is the mastermind? Haymitch. The lush. Who suffers from DTs, so he's not faking the drunkenness.
Turns out Finnick isn't really a narcissistic playboy, and Johanna's bitchiness is most likely a product of and/or cover for her inner Broken Bird.
In the Matador Series by Steve Perry, Sleel is initially portrayed as a Loveable Rogue* one of his friends actually used the words "loveable rogue" to describe him with a complex about always proving he's the best. Then he's found browsing in the philosophy section of a bookstore, casually quoting poetry, and being able to spot a deception that fooled everyone else in his team. And then it's revealed that he has a doctorate in poetic literature, wrote several best-selling novels, and used the proceeds to set up a foundation caring for orphaned children. Oh, and his name is actually an acronym of his neglectful parents' initials.
"You are thinking, Kull," said the old statesman, suddenly, "that Ka-nu is a useless old reprobate, fit for nothing except to guzzle wine and kiss wenches!" In fact, this remark was so much in line with his actual thoughts, and so plainly put, that Kull was rather startled, though he gave no sign. Ka-nu gurgled and his paunch shook with his mirth. "Wine is red and women are soft," he remarked tolerantly. "But—ha! ha!—think not old Ka-nu allows either to interfere with business."
In The Tillerman Family Series by Cynthia Voigt, it's quicker and easier to count the characters who do not have Hidden Depths than it is to count the ones who do. Nobody is exactly who or what they seem at first, and reputations and early judgments frequently turn out to be unfair, flawed or flat-out wrong.
The 3 cops of L.A. Confidential. Bud is frustrated with being the Dumb Muscle, Exley is a squeaky clean hero cop ready to sell anyone out for a promotion, and Jack wants to do real cop work, but he's so hip deep in corruption that's it's hard to escape.
In The Pale King, Chris is surprised when his father quotes a famous poem by Percy Bysshe Shelley. The again, he didn't know much about his father in the first place...
Rafael Gives Light in Gives Light is the son of a serial killer, a brooding loner known for getting into fistfights, but he leaves memorials at the graves of his father's victims.
In the Carl Hiaasen book FlushJasper is the son of the main antagonist, and serves as the protagonists jerkass rival, along with his crony Bull. Bull is described as very big, but not too smart (and he is beaten by the protagonist's sister and grandpa). However, later in the book, Jasper and him sneak out some beers and cigarettes, which he tried to light up, and instead set his dad's boat casino on fire. Bull drags him out of the burning wreckage, despite both inhaling smoke, and Jasper even tries to shift blame on to him for it. Amazingly, he still hangs out with Jasper, and leaves him when confronted by protagonist and his family in the end.
In the Red Dwarf novelisations, the character of Arnold J. Rimmer is fleshed out with lots of backstory that explains why he is such a Jerkass as an adult. Sociopathic parents, bullying siblings, thwarted expectations, plus a couple of honest mistakes anyone could have made (Gazpacho soup...) but which paralyse him with embarrassment and reinforce his self-loathing. He becomes more sympathetic as a result; you end up feeling sorry for him.
And his alter-ego "Ace" Rimmer demonstrates what really is there, deep down, and what Rimmer might still have the potential to become.
Horus Heresy: Perturabo has, before "Angel Exterminatus", either been ignored entirely or portrayed as the bitter siege specialist his Legion is known for being. In that book, however, it turns out that he has a solid grounding in his homeworld's classical mythology, and his greatest dream is to build cities, universities and monuments, rather than grey slabs encrusted in guns and barbed wire. A lot of his bitterness came about because nobody, including his father the Emperor, actually cared enough about him to learn this.
The Gentleman Bastard series is all about this: on the surface, the Gentleman Bastards are ordinary sneak thieves, while they're really brilliant confidence artists. Their original leader, "Father Chains," masquerades as a blind priest, but is really a gifted forger and all-around criminal, who's pulling the wool over the eyes of the town's crime kingpin.
And in the second book, they run into a pirate captain who's also a highly-educated student of literature.
Throughout most of the Amber Brown series, Amber dismisses the possibility of ever being friends with a classmate of hers named Fredrich Allen because he picks his nose and chews the boogers, and she doesn't think she could ever be friends with someone who does that. In Amber Brown Is Tickled Pink, however, she meets him at his father's farm and comes to realize pretty quickly that the picking and eating is just a bad nervous habit, rather like how she sometimes chews on her hair or her nails, and learns that Fredrich is actually a pretty nice boy. After this, she becomes very annoyed with her other friends when they tease him behind his back, just like she used to do with them, only now she feels guilty about it.
B's father in the Zom-B series. At first, he seems like nothing more than a wife-beater and a violent racist. But at the end of the first book he storms B's school and saves as many of the kids as he can. And later he expresses that he really does love his wife, by choosing to die with her.
In Michael C. Bailey's Action Figures - Issue One: Secret Origins, Matt comments that Carrie has these when she says ice hockey is her favorite sport.
Wax And Wayne: Steris initially comes off as a stoic, fussy, and small-minded woman obsessed with paperwork. Over the course of the books, it becomes clear that she's both more fragile and more empathic than she seems, plus a teeny tiny adrenaline fetish. In Bands Of Mourning, she is extremely nervous before the wedding, and reveals that while she knows she can't plan for everything, she at least feels better for trying.
A recurring theme in The First Law series. Some characters who at first appear as nothing more than villainous scumbags will turn out to be more noble than we were originally led to believe or they'll reveal to have good reasons for their actions. Not unlikely, some of the "heroes" will be revealed to have a darker side to themselves or that they have been working on very selfish motives.
Prominent in A Man Called Ove. The title character seems, at first glance, like nothing more than a bitter old curmudgeon. As the story goes on you learn a whole lot more about him and realize what is beneath that exterior. In fact, the point of the story is not that Ove needs to change but that those around him need to learn to look deeper.
Then there's the fact that ultra conservative Ove turns out to have no issues whatsoever with homosexuality, and even allows a young man called Mirsad to move in to his house after Mirsad came out to his father and got kicked out of the house.
In The Dinosaur Lords, it turns out that every girl in Melodía's Girl Posse has hidden depths, leading to Melodía (who for most of the book thought herself the smartest) to conclude that she's the only shallow one out there.
Abigail, apart from being a cynic who likes to see others suffer, is also an excellent strategist and planner, not to mention a born spymaster.
Llurdis talks dumb, but is the most caring one and willing to go through literal shit to save her friends.
Lupe is foul-mouthed, but also caring and devoted.
Fina is a crybaby with a new great cause every other day, but she's also highly analytical and intelligent.
Journey to Chaos: Would you believe that Annala, the shy and Cute Bookworm, is/was a daredevil? Her Mad Scientist mom made her self-mending clothes because of it. It relates to her Crisis of Faith. Taking extreme risks and allowing her Healing Factor to repair her body when the risks fail was how she reassured herself that she wasn't forsaken by her race's patron goddess.
One scene in Way of Kings has her counting to ten heartbeats, which "means what you think it means". A shardblade takes ten of the owner's heartbeats to summon. The scene means she has one, each of which are considered priceless and rare. Given her culture's sharply defined gender roles, it's practically unheard of for a woman to have one, much less someone with the image she tries to present in public.
Due to her flighty and friendly nature, a lot of people (especially Kaladin) assume she lived an easy and pampered life. Ha.
Shallan: You don't realize it, but you just said something very very funny. Kaladin: Then why aren't you laughing? Shallan: It's not that kind of funny.
Normally, she's cheerfully shy and demure, but when a true life or death situation comes up, she turns into a stone cold killer. She killed her mother as a child with the Shardblade said mother was trying to take from her, strangled her father with the necklace he bought her, and stabbed Tyn (her conwoman mentor) through the heart after a short fight.
Tyn: Sometimes, we must do things we don't like, kid. Difficult things. [Shallan summons her Shardblade and kills Tyn] Shallan: Difficult things. Yes. I believe I told you. I've learned that lesson already. Thank you.