20,000 Leagues Under the Sea: Exaggerated with Conseil, The Professor Aronnax's servant. He risks his life to save his employer not once, but twice in the novel. When Aronnax talks with Ned Land about the Great Escape, Lampshaded when Conseil considers himself one with his master's decision.
"Your friend Conseil," the fine lad replied serenely, "has nothing to say for himself. He's a completely disinterested party on this question...He's in Master's employ, he thinks like Master, he speaks like Master, and much to his regret, he can't be counted on to form a majority. Only two persons face each other here: Master on one side, Ned Land on the other. That said, your friend Conseil is listening, and he's ready to keep score."
"I couldn't help smiling as Conseil wiped himself out of existence."
Subverted with Noor. When Raphael is sent to Armelia, Noor begs to go with him, supposedly because of this trope. Actually, though, he's a spy who's supposed to keep an eye on Raphael.
Tanya plays this straight. Having been saved by Iris as a child, she is loyal to Iris and claims to serve her only.
Shadowcatch takes his oaths seriously (in fact, those who willingly break them are a bit of a Berserk Button to him). As such, when he pledges himself as Tyr RuGaard's bodyguard, he stays utterly loyal even after RuGaard is ousted in a coup and exiled, following him into it. Years later, he says that he still considers RuGaard the only real Tyr.
There's also RuGaard's pet bats. They might be easily bribed with blood meals from other dragons, but they're ultimately loyal to their original benefactor. This is best shown during the Final Battle with Infamnia and Rayg, who betrayed RuGaard, seemingly to his death. The bats end up swarming the two en masse, with shouts of "Revenge for our Tyr!", contributing to their demise. AuRon comments on his brother's ability to inspire loyalty in others, and seems impressed by it.
Boxer, the horse in Animal Farm. "Napoleon is always right." Unfortunately, Napoleon didn't return the sentiments... Particularly tragic because the reason Boxer outlived his use was he was working extra hard to please Napoleon.
Here lies our leader In the dust of his greatness Who leaves him now be shamed forever I who am old will not leave this battle But will lie by his side in the dust with my Master
Gunner Ferik Jurgen is completely loyal to Commissar Ciaphas Cain, HERO OF THE IMPERIUM, who trusts him more than himself (because he "knows"he isn't as trustworthy as people say). Jurgen will obey any order from Cain, no matter how crazy it sounds.
In Dangerous Spirits, Konstantine retains his loyalty to the Tsars even a hundred years after his death during the Revolution.
Don Quixote: Sancho Panza claims to be this for the main character, but there are limits for patience when in the service of a Lord Error-Prone who always manages to get himself and Sancho in an Humiliation CongaOnce A Chapter. Several times in the book, Sancho considers leaving Don Quixote's service, but he is so fond of him he never does it.
"...if I were wise I should have left my master long ago; but this was my fate, this was my bad luck; I can't help it, I must follow him; we're from the same village, I've eaten his bread, I'm fond of him, I'm grateful, he gave me his ass-colts, and above all I'm faithful; so it's quite impossible for anything to separate us, except the pickaxe and shovel."
The Dresden Files: Harry Dresden and Thomas Raith, the first because he never had any family aside from his father who died when he was small, and Thomas because his family was so messed up that he always protected his siblings, and that was the attitude Lord Raith instilled in his family (as a method of control), especially, his younger siblings, i.e. Harry and Inari. Family is important.
Harry: [in Proven Guilty when they are about to attack Arctis Tor and, having given a you-don't-have-to-come-with-me speech, his companions all step forward] I don't care whose DNA recombined with whose. When everything goes to hell, the people who stand by you without flinching — they are your family.
In the later books, he develops this with Murphy, too.
Murphy: Don't you start taking the highway to Hell. Because I'm going to be right there with you. All the way.
Molly to Harry. Harry's not too happy about this, given all of the questionable deeds she's done for his sake. Mab goes so far as to compare him to his old Evil Mentor Justin.
In Dune, the servitors of the Atreides except Yueh are loyal to their House. And even Yueh took steps to ensure that Paul and Jessica would survive his betrayal. Duncan Idaho sacrifices himself to buy time for Paul and Jessica's escape, Gurney Halleck quickly renews his service to Paul when he discovers he is alive, and Thufir Hawat kills himself rather than follow through on orders from the Emperor to kill Paul.
Thufir: You see, your Majesty? See your traitor's needle? Did you think that I who swore my life to the Atreides would give them less now?
The Atreides dukes are similarly loyal and protective toward their retainers. Paul Atreides is even willing to sacrifice his life to save the much, much older Hawat:
Paul: For I say to you, Thufir, that in payment for your years of service to my family you may now ask anything you wish of me. Anything at all. Do you need my life now, Thufir? It is yours.
And it's ironically the Atreides' ability to command this sort of fanatical loyalty which makes the Emperor nervous enough for his own throne to assist the Harkonnens in their overthrow in the first place.
LucaBrasi from The Godfather has this towards VitoCorleone. In the backstory it is mentioned that during the Olive Oil War some mobsters tried to kill Vito and Luca proceeded to go on a Roaring Rampage of Revenge that only ended when Vito became well enough to call him off. However, this trait ultimately backfires on him when Vito has him pretend to leave the Corleone family to infiltrate a rival mafia family and they see right through it.
EarthCent Ambassador: Beowulf is a Huravian hound, one of the most loyal race of dogs in all the galaxy, they are even loyal after their dead, they are able to reincarnate and go in the search of their former master wherever he/she is.
Melanie Wilkes towards Scarlett O'Hara in Gone with the Wind. It doesn't matter what Scarlett does, what social norms she breaks, or how uncomfortable Melly might feel about some of these things. She is Team Scarlett 100%, and she will cast aside people she has known and loved since childhood if they speak against Scarlett. She doesn't seem to notice that Scarlett for a long while despises her — they are sisters-in-law and family and to Melly, that's that. Of course, it helps that Melly is the only one who was there and saw everything Scarlett suffered and all the sacrifices she made so that those in her household could have food, clothing, and a roof over their heads.
Harem in the Labyrinth of Another World: Roxanne is so devoted to Michio that when he tried to arrange for her to be set free if he dies, she insisted that she'd rather be dead than not have Michio as her master.
Hagrid is extremely loyal to Dumbledore in Harry Potter, probably more so than any other person. It is mutual, too. Dumbledore outright tells Professor McGonagall that he trusts Hagrid with his life.
Sirius Black has put himself through a lot out of loyalty to Harry and his (now-deceased) father, who was Sirius's best friend.
Possibly the best example of this trope in the series is Severus Snape. Readers (and every character, except for Dumbledore,) don't learn of Snape's loyalty, sacrifice, or the circumstances of it until the end of the last book, though it has defined him the whole time. In addition to Snape's loyalty to Dumbledore, he devoted the rest of his life to protecting Harry Potter, the son of his lost love Lily, and ultimately dies in his efforts to save him.
Also, Ron's loyalty to Harry is repeatedly mentioned. They have a couple of instances where they're on the outs (they are teenage boys), but on the whole they're practically brothers, and Ron stands wandless on a broken leg to get in between Harry and someone he thinks is trying to kill him in PoA saying they'd have to kill him to get at Harry. The "practically" is erased after Harry marries Ginny in the epilogue as they become brothers-in-law.
Harry's loyalty to Dumbledore is tested throughout Books 5, 6, and 7. Even after learning about Dumbledore's Dark and Troubled Past and his Feet of Clay, Harry's loyalty to his mentor is unquestionable. "Dumbledore's man, through and through" indeed.
Villainous example: Bellatrix Lestrange is completely loyal to Voldemort, to the point of proudly going to Azkaban for him. Ditto Barty Crouch Jr.—at least after his time in Azkaban hardened him, before which he denied involvement (in the same crime for which Bellatrix was sentenced, incidentally) and begged for release.
In The Heroic Legend of Arslan, Arslan eventually wins the admiration and respect of his followers by his own merit. Farangis sums it up perfectly.
Farangis: His Highness, the Crown Prince, is always making an effort. It is merely that this fact is obvious to those who serve him. It is because we see him as a man to be treasured that we are all happy to serve him.
This actually becomes a plot point. Andragoras became (understandably) paranoid when he noticed how popular Arslan is with the remaining Parsian generals and officials and how they are possibly becoming more loyal to Arslan than to the king himself. That is partly the reason why Andragoras decided to send Arslan away to Port Gilan, essentially exiling Arslan in all but name. Indeed, majority of the generals are dissatisfied when Arslan is forced to leave.
Andrew LaFollet in Honor Harrington is the titular character's personal armsman, sworn to die for her service if necessary. Despite Honor's trying to save him as the last surviving original armsman by having him guard her son, he dies saving his cousin and Honor's son and mother
Not just Andrew, but ALL of her armsmen display this. It's a 100% volunteer service and they all joined as they feel they owe a personal debt to her.
Then there's Horace Harkness' loyalty to Manticore. Caught, given a chance to surrender and or die, he switches sides. Then proceeds to manipulate his keepers until he can personally free his commander in a rather epic way.
On the Havenite side, we have Eloise Pritchart, who goes from being a Commissioner and one of St. Just's favorites at that, but is really loyal to the Aprilists and the true Republic of Haven, and becomes the first President of the restored Republic of Haven.
We also have then-Citizen Commander Shannon Foraker, who single handedly, without warning her CO, saved 12th Fleet from State Sec. Oops.
Peeta Mellark towards Katniss Everdeen in The Hunger Games. Their mentor Haymitch notes after their first arena that there was no point in trying to save Peeta because he didn't want it — he wanted Katniss to win. Even brainwashing (or "hijacking") designed to make him hate and fear Katniss, essentially turning him into a weapon against her, is able to change this for more than a few weeks or months at the most. This in comparison to every other person who has been subjected to this — Peeta is the only one who has been able to overcome it.
I Swear I Won't Bother You Again!: Marin is fiercely loyal to Violette and loathes the Vahan household - especially Auld - for their wretched treatment of her mistress and the misery she experiences while living under their roof. The only reason she's serving the Vahan family and following their orders is so she can protect Violette and watch over her.
Lord Byron wrote a poem dedicated to a beloved dog who died of rabies titled Epitaph to a Dog. The dog's unflinching love and loyalty are described in great detail:
But the poor Dog, in life the firmest friend The first to welcome, foremost to defend Whose honest heart is still his Master's own Who labours, fights, lives, breathes for him alone
A Legacy of Light: Sermekhet faithfully serves his master, Pharaoh Tutankhamun, finding his loyalty to the king warming into friendship, even brotherhood.
The Lord of Bembibre: Don Álvaro earned his squire's absolute loyalty and devotion when he risked his life to save Millán from drowning in a river.
Aragorn, Gimli and Legolas spend several days giving chase on foot to the orcs who captured Merry and Pippin. Aragorn outright states that they will continue looking for them even, if in the end, all they can do for them is starve to death together.
Also, Merry towards Éowyn, Éowyn towards Théoden, and Pippin towards Faramir.
The Goblins of Goblin-town in The Hobbit to the Great Goblin even after he is killed by Gandalf trying to save the Dwarves and Bilbo. The Great Goblin and his minions believed the Dwarves were plotting against them when they discovered the Dwarves in their territory, but we know they were really trying to head to The Lonely Mountain to confront Smaug the Dragon and they were further incensed when the Great Goblin saw the blade that slew many Goblins beforehand in possession of Thorin. When the Great Goblin was killed, all the other Goblins with their Wargs followed Thorin's company both to avenge their ruler and [[spoiler: and believed they were more of a threat when Smaug was killed and the Dwarves' treasure was reclaimed. The Goblins ultimately lose the battle of Five Armies to the allied Dwarves, Elves, Men, and Eagles but still manage to kill Thorin, Fíli, and Kíli.
Spinnock Durav from Malazan Book of the Fallen will do pretty much anything Rake asks him to, even if that means not acting on his newly discovered feelings for Salind, or having to fight Kallor for a whole night straight.
There are two examples in The Mental State. One of them is 'Big Billy', who promised a relative that he would always protect his brother, 'Little Mickey'. The other is Charlie, a naive inmate who is hopelessly devoted to Zack, on account of him being the only person who has ever stood up for him and tried to understand him. He is so loyal, that he is completely impervious to manipulation by anyone else, including a devious psychopath revealing Zack's darkest secrets to him.
Nightfall (Series): A villainous example –- Tristan is completely devoted to Vladimir, so much that many call him the Prince’s puppy.
Oliver and the Seawigs: Stacey de Lacey's sea monkeys are fiercely loyal to him, and will do anything he asks of them. At the end, when Stacey de Lacey is rowing away following the Thurlstone's death, his sea monkeys come to him and start sitting on his raft. When it runs out of space for more, the sea monkeys start climbing up Stacey's body, which he is not happy about.
In Percy Jackson and the Olympians, this is the titular character's Fatal Flaw. It is repeatedly stated that he would watch the world burn if it meant saving his loved ones. Thankfully, by the end of the series he manages to overcome this flaw.
In Super Minion, a lot of members of Hellion's Henchmen are just there because it's a job which pays really well, but a lot of the old guard are fanatically loyal to Hellion personally, because they remember how bad things were before she took power.
Giacomo, the protagonist of Rebel Geniuses, is revealed to be a Tulpa, an artistic being of destruction near the end of the book. Instead of treating him coldly like they had before (though Aaminah had been friendly), his new friends (especially Savino, who is The Rival for Giacamo) decide that he's ultimately their friend, and they start seeing Tulpa in a different light.
Gaara Hiden: A Sandstorm Mirage: Gaara earns Shijima's unwavering trust and loyalty when he lets Hakuto and Shigezane go and live in Konoha under new identities.
Dr. Watson to Sherlock Holmes. He repeatedly risks his life to accompany Holmes, puts up with repeated cruel manipulations and deceptions from the man with little reaction except relief that Holmes is safe, and adamantly refuses to leave whenever Holmes suggests that what they're doing might be dangerous/illegal/insane and that Watson would be safer staying out of it. Once he even forces Holmes to take him along on a burglary, when Holmes is reluctant to risk Watson getting thrown in jail too if they're caught, by threatening to turn Holmes in himself. He doesn't only exhibit this loyalty towards Holmes, though — Watson also muses about being willing to die for Sir Henry Baskerville about three days after first meeting him, and vows to dedicate his life to searching for Mary Morstan's lost treasure equally quickly, even though it would put her far out of his league.
The Devil’s Dust by James Lovegrove sees Sherlock Holmes and Doctor Watson joining forces with Allan Quatermain and Umslopogaas to investigate events involving the death of Quatermain’s son in Africa. When Umslopogaas tells of the circumstances of Henry Quatermain’s death, he also reveals that he travelled all the way from Africa to England to give the news to Quatermain directly, feeling that such information could not be conveyed by telegram but must be delivered in person, despite Umslopogaas not having spoken directly with Quatermain for some years by that time. Holmes and Watson each express understanding and approval of the other man’s loyalty to his friend.
Song at Dawn: According to Raoulf, all soldiers should have this for their liege lord.
Raoulf: She's just a woman. He's your liege Lord, my boy, and if it was you instead that he wanted, Viking fashion, why, you'd just have to bend over and take it.
Davos is forever loyal to King Stannis Baratheon even after losing four sons in Stannis's service.
Catelyn orders Brienne to bring Sansa back to her from King's Landing. By the time Brienne arrives, Sansa is no longer there, so Brienne starts searching for Sansa desperately despite the dangers of the road and the fact that Catelyn is already dead by the time, and there is no safe place Brienne could bring Sansa to anyway.
The entire North ( except for the Boltons and possibly the Karstarks, Ryswells, and Dustins) exhibit this trope toward the Starks. The Northmen, both lords and smallfolk alike, are willing to march through blizzards and bone-chilling cold in a state of near-starvation or just keep on fighting even when all hope is faded for the sake of the Starks. Special mention goes to House Manderly. The North's loyalty to the Stark family is the reason why King Stannis Baratheon wants to legitimize Lord Eddard Stark's illegitimate son Jon Snow (who was openly raised by Eddard as his son alongside his trueborn offspring) so Stannis can win the North's support via a son of Eddard Stark — Jon — but Jon turns Stannis down out of loyalty to his father's gods, duty to the Night's Watch, and for the sake of his half-sister Sansa's claim on Winterfell. Special mention should also go to Greatjon Umber, who is one of Robb's staunchest supporters and is furious if anyone even insults Robb.
Like the Northern Houses, the Vale Lords are completely loyal to House Arryn — particularly to Jon Arryn and, by proxy, to his son Robert Arryn.
The Kingsguard are supposed to be this in regard to the King of Westeros. The last member of the kingsguard who actually did that was… maybe Ser Arthur Dayne?
Nico and Josef are insanely loyal to one another, to the point that either is perfectly willing to put the fate of the entire world on the line for the other's sake.
For Miranda, her spirits will openly defy their all-powerful goddess.
Mara Jade isn't the kind to give away her loyalty easily, but when she does, she'll defend whatever she chose with her life. She tends to be loyal to specific people rather than a large group; to Palpatine as an Emperor's Hand, to Talon Karrde as a smuggler, and to Luke and Ben as a Jedi, wife and mother.
Luke, Leia and Han of the Original Trilogy qualify even better. It's what Palpatine used to tempt Luke to fall to The Dark Side, and almost succeeded.
In Sweet Piglet, we have this with the piglet, after its master dies. The Piglet often visited it's Master's grave and would lay flowers on it, continuing to do so until it dies in the end.
The first book of The Sword of Truth series is dealing with a ritual the Big Bad uses to get into the world of the dead and back. It involves brainwashing a young boy into complete loyalty, killing him (by making him drink molten lead), and then using his spirit to travel to the underworld and back. As a case of exaggerating the trope, the boy must remain loyal until the traveler returns. In a later book, Richard uses this ritual as well, except he already had a spirit loyal enough to him since book one.
The Wandering Inn: The Seven never stopped being loyal to Flos, the King of Destruction, even when he lost all motivation, and for 10 years just sat on his throne, letting his kingdom slowly waste away.
Wolf Hall portrays Thomas Cromwell as being very close to Cardinal Wolsey. After Wolsey is kicked out of his office and exiled north for failing to get Henry's marriage to Catharine of Aragon annulled, Cromwell spends most of his time trying to restore Wolsey to the King's good graces — unsuccessfully, and Wolsey dies on a journey back to a trial for treason. Cromwell often thinks about Wolsey and what he would do in a given situation and still refers to him as his "master". Later, when the King wants Anne Boleyn gone, Cromwell uses the opportunity to avenge Wolsey by having the five men who he deems most responsible convicted and executed alongside her.
. The dog's unflinching love and loyalty are described in great detail:But the poor Dog, in life the firmest friend