In Nineteen Eighty Four, this is one of the things Big Brother wants you to be. At first glance, one might think that since Oceania is at war with Eastasia, it's natural that they'd want patriotic and devoted soldiers. However, as O'Brien tells him in then end, the Forever War between Eastasia and Oceania is of no importance at all, and merely one more way for the party to control the people. So in effect, this is what Big Brother encourages people to become.
In Terry Mancour's The Spellmonger Series, almost every single one of the warmages from the first book are this, including the main character.
In Adam R. Brown's Astral Dawn series, Tyr derives pleasure from battle, death and destruction. The only reason he's involved in the plot to conquer Heaven with Set and Devlyn is because it will give him more opportunities to fight and kill.
The main character in Dis Acedia, Shroud, develop into one, but Brina turns out to be outright addicted to warfare.
In Dragon Bones, Ward mentions this as the reason why his father fought in the king's wars so valiantly, even though he hated the king's guts - he just enjoyed fighting so much. Ward himself gets into the mindset, too, and is rather disturbed by it. He doesn't make it a lifestyle. Averted with his aunt and tactical advisor, Stala, who is strongly opposed to fighting for the sake of fighting, and advises him to only fight if he's clearly stronger (or has a bigger army) than the opponent.
Lord Borel, in Roger Zelazny's The Chronicles of Amber, has as his main goal in life to outfight either Eric, Corwin, or Benedict, some of the other best swordsmen in that universe. Corwin shows him that it's not all about bladework.
The Jalis in Deltora Quest are a race (or tribe) of Blood Knights, who relish combat and live for battle.
The "Warriors at the End of Time" in some of Michael Moorcock's fantasy novels (particularly The Dragon in the Sword) are said to be powerful soldiers who loved fighting for its own sake, and were then damned to fight on behalf of the Cosmic Balance for all eternity.
Sekhmet, in Matthew Laurence's Freya series, is wholly and completely this, right down to licking the blood of her foes off her hands after massacring them.
From the Reboot Book Series, Wren 178 is stated to enjoy "the hunt" - the hunt of humans, that is.
Keeping in step with the trope's title, Radha of Keld in Magic: The Gathering'sTime Spiral card set and novels was intent on little other than fighting, at first spurning the world-saving efforts of Teferi and his companions... at least until he gave her the ability to kick even more ass than she could previously. She softens a bit as she grows to accept the necessity of helping Teferi, but she's always a hard-bitten warrior first and foremost. To wit:
"I hope to have such a death - lying in triumph upon the broken bodies of those who slew me."
In several of the later Animorphs books she narrated, Rachel expressed fear that she might be slowly becoming like this. Too bad she was this soon after acquiring her grizzly bear form. Seriously. She and Zaraki up top would make a lovely couple.
In The Dresden Files novel Cold Days, Harry finds that the Winter Mantle has a very strong drive for this. In fact, after a major battle, Karrin says he had an erection throughout the battle. Suffice it to say, the change very much scares the person.
The Silastic Armourfiends of Striterax in The Hitchhiker's Guide to the Galaxy took this to extremes since if one was locked in a room by himself he would eventually beat himself up just for something to do.
David Eddings' The Elenium and The Tamuli trilogies had the Atans, a race who bred themselves as fighters— but did so a little too well, giving them hair-trigger violent reflexes, so that their society was plunged into endless war until they voluntarily pledged their entire race to slavery to the peaceful Tamuli, who as a result gained an unconquerable empire by default. Every Atan believes that they have to have a master to hold them back, or they go on killing sprees.
The Nac Mac Feegle in the novels are clans of "pictsies" who live primarily for drinking, fighting, and stealing, preferably at the same time. Each clan also has a Gonagle or Warrior Poet, though in this case the poetry itself is a weapon of war. Taken to extreme when it's explained that a Feegle left all by himself may very well kick himself in the nose just to keep himself occupied.
There's also the D'regs, a nomadic tribe from the desert regions of Klatch characterized by their love of fighting. It's said the D'reg word for "stranger" is the same as their word for "target". There is one scene in Jingo where someone has a hard time translating the concept of "fighting for freedom", since in the D'reg language they are the same word. It's also mentioned that when the nations of Klatch and Hersheba drew an arbitrary border across the D'Regs home desert, they leapt on this new division of nationality as a wonderful excuse to start fighting each other, too.
Strong Belwas, a former pit fighter, delights in showing off his prowess to the point that he always allows his opponents to get one slash in before he kills them.
House Clegane has spawned two—Sandor Clegane lives for little other than fighting and believes that "killing is the sweetest thing there is", and he's the good brother.
Gregor Clegane managed to make a career out of raping and murdering his way across Westeros, referred to as "foraging" in polite conversation. Though unlike a true Blood Knight, he doesn't like fighting opponents who can actually put up a good fight. He likes killing people, not fighting them.
The Dothraki. They consider any event (like a wedding) with less than three deaths a dull affair.
The Smiling Knight was an Ax-Crazy Blood Knight who wanted to fight a member of the Kingsguard. He got his wish and met his end when he fought Arthur Dayne, the Sword of the Morning. Jaime witnessed the fight in his youth and considered it one of the best moments of his life. In a moment of self-reflection in the present, Jaime wonders how the boy who wanted to become the Sword of the Morning became the Smiling Knight instead.
Robert Baratheon, before he was King he was warrior who lived to fight, and when he took the Iron Throne he grew bored of managing the realm. He would have left the throne, and sailed to the Free Cities to be a sellsword. The only thing stopping him from doing it is his (bastard) son Joffrey taking the throne.
The Heroes by Joe Abercrombie has two big ones: Bremer Dan Gorst of the Union's entire existence is fighting to the point where he compares fighting one-on-one with another enemy to romantic affection. The other one is Whirrun of Bligh who actually faces off against the former. Gorst is extremely disappointed when it ends prematurely.
Mace Windu struggles with this in the novel Shatterpoint. You don't get to be second-in-command of the Jedi Order by going to town on everyone with a lightsaber, and Windu loves the stability the Republic provides, but he likes fighting anyway. He develops the dangerous lightsaber style known as Vaapad as a way to channel this aggression for good purposes.
The Yuuzhan Vong warriors live for combat, justified as they are raised in a caste system, and they live solely to fight and kill.
Jacen Solo AKA Darth Caedus is a lead from the front, get-stuck-in kind of fighter. It catches up with him in the end however, as the intensifying pace of battles leaves him increasingly debilitated.
Tash's first clone in Galaxy of Fear, is this as well as being Drunk on the Dark Side. So are the others, but she's specifically happy at the chance to kill Tash right then and there.
Greystone Valley's villain Baelan is a ruthless warlord who has grown frustrated with the fact that he's trapped in a world with nothing worth conquering. The entirety of his villainous plan is focused around opening up infinite other worlds where he can do battle.
99.99% of the Drow race from R.A. Salvatore's Drizzt novels (and Dungeon & Dragons in general) are Blood Knights. They are born, raised, and die (usually before anything close to the natural end of their 700+ year lifespan) in a perpetual power struggle featuring hundreds of noble houses. And ninety nine percent of them (with the exception of Drizzt, his father, and a couple others from other scenarios, and they partially meet this tropes standards in the sense that although they don't kill for fun they get fun from killing), live for it and enjoy every second of their blood-soaked lives. Even Drizzt is a Blood Knight to a certain, less evil extent: in one of the long introspective commentaries placed at the opening of each act, Drizzt comes to realize that he is a "creature of action": he can only be truly content if he has his swords strapped to his waist and is going somewhere, though this is more of a thirst for adventure than a true hunger for battle. He has, however, been known for bouts of berserker rage when the right buttons are pushed. Drizzt's rage does not hinder his incredible focus in the slightest, and makes him hundreds of times more dangerous to even disciplined foes.
Speaking of R.A. Salvatore's novels: Artemis Entreri. The most Blood Knighty Blood Knight of all Blood Knights!
The most wild battle rager Thibbledorf Pwent! He is a blood knight personified!
All the Brothers in J.R. Ward's Black Dagger Brotherhood series fit this trope. They're elite vampire warriors bred to protect the vampire race from vampire hunters and they love their job. All of them, but especially Zsadist, live for fighting and killing — until they meet a good woman because Love Redeems.
In Alan Dean Foster's The Damned novels, all of humanity were Blood Knights. It turns out that the humans only fought each other because they lacked an external enemy to fight. When such an enemy presented itself...
Kage in Gav Thorpe's Warhammer 40,000 The Last Chancers. At the end of 13th Legion, he receives a pardon, resolves to stay in the forces outside the penal legion, and shortly thereafter loses it by brawling. In Kill Team, he is told that he used up his last chance and will never be pardoned again, and he can cope, realizing that he would have ended up fighting again.
Conan the Barbarian is a straight-up example of this trope. He comes from a culture of northern barbarians who consider the thrill of battle to be one of the only true joys in life.
The Valerians of the Lensman universe are this - seven foot tall denizens of a three-grav world, whose favourite weapon is the space-axe (because personal shields increase their resistance with the velocity of the impacting body), whose ultimate goal is a warrior's death, and for whom a peaceful death is a disgrace. As Smith himself says: "No bifurcate race, and very few others, have ever willingly faced the Valerians in hand-to-hand combat." Fortunately they are the good guys, and more fortunately they are very good at recognising authority (in terms of who to kill and when to stop).
The Rohirrim in The Lord of the Rings, And then all the host of Rohan burst into song, and they sang as they slew, for the joy of battle was upon them. Not to mention when they later charge at the, far numerically superior, enemy screaming "Death!".
The warships and militarised drones of The Culture all exhibit this to some extent. They have exceptional self control but when they feel that circumstances are such that they can let themselves off the leash they will utterly annihilate their opponents and have enormous fun doing so. In at least a couple of cases, they've been known to keep very high resolution recordings of the battles they're involved in that they seem to get an almost sexual thrill from watching later.
Trapped on Draconica: All Leondians love fighting. This means their Prince, Kalak, will always choose fighting over any other solution.
Wild Cards. Billy "Carnifex" Ray is this, displaying increased strength, speed and healing abilities to get him back in the fight. This is a man who once pursued an opponent with half of his face cut off, and seems to revel in combat. Considering that he's an Expy of Wolverine, it's not surprising.
In John Milton's Paradise Lost, when the devils take council, Moloc is the first to speak and urges immediate and outright attack.
Sculley from 1356, who is very upset to realise he hasn't killed anyone in at least a month.
In Musashi, the titular character and his Foil, Sasaki Kojiro are both this. However, Musashi fights in order to test himself and become a master, while Kojiro has a sadistic streak, and fights to promote his name.
The trollocs of The Wheel of Time are what happens when Blood Knight meets Dirty Coward. They're extremely bloodthirsty and love to fight, but really don't seem psychologically equipped to deal with defeat. So when they're winning, they're inhumanly aggressive and brutal, and when they're losing, their morale breaks almost instantly and they route easily. Whip-wielding Myrddraal ensure that no matter which mode they're in, trolloc forces remain pointed at the enemy.
Most of the Career tributes in The Hunger Games, who are trained from childhood to fight and to treat the Games like a game and an honorable tournament. They usually proudly volunteer at the reapings, something most kids from the lesser districts would never consider doing.
Mayor Prentiss. When he witnesses an army vastly superior to his own descending upon his city with the intention of killing him in retribution for a genocide that he committed for the sole purpose of instigating this war his reaction is to grin with joy and utter: "War. At last."
In Riesel Tales: Two Hunters, one of the two titular hunters, Runge Margavo, is more than happy to snatch up an assassination job and repaint the floor with someone's gray matter, and he's been described as someone who participates in bar fights with apparent regularity.
T. Sean Collins, the mercenary, in World War Z. He realizes that he is "addicted to murder" and will eventually either kill himself when he runs out of zombies to kill or face losing control and slaughtering actual people.
Skeeter Traps from Chronicles Of Magic is a ten year-old version of this. While one of the good guys, she enjoys fighting and is naturally prone to violence.
Cecily Herondale from The Infernal Devices, is a milder example of this. Gabriel Lightwood notes that she seems to enjoy fighting.
Several villains from Dragonlance qualify as this - mainly Kitiara, the very deadly Femme Fatale, but also Ariakas, the goddess Takhisis and all villains of the Istar arena.
Talia in The Princess Series. When Snow first meets Danielle, she mentions how happy she is to have someone to talk to besides Talia. When Talia tells her to be quiet, Snow explains that Talia is only happy when she's stealing something or beating people to a pulp,
Heat from Quantum Devil Saga: Avatar Tuner has no problem accepting to his new demonic form and as a result, likes to rush headlong into battle to soothe his blood-thirst.
Snowflake from Winter's Tale (Emrys Vaughn) claims to be literally addicted to violence, going into withdrawal if she goes more than a week without getting into a fight.
Katja in Eli Freysson's The Silent War is one of the setting's fated demon hunters, and so was quite literally born to fight. Her love of brawls meant every boy in the village feared her by the time she was twelve, and she is occasionally disturbed by the degree to which she enjoys bloodshed and danger.
The Stormlight Archive: The Alethi people used to be a Proud Warrior Race charged with protecting the other nations from the Voidbringers, but when the Voidbringers were finally defeated, the Alethi never gave up their arms. Over four and a half thousand years later, the fighting is all they have left. The ideals of competition have pervaded every aspect of their society (even their religion has a points system), and they consider war the greatest of arts. Several times in the series, Alethi are asked "Why are we fighting," and the Alethi look at the asker like they're crazy. This is all made worse by the "Thrill," a nationwide bloodlust that afflicts the Alethi elite in battle, blunting the worst aspects of war even when they're on the front lines themselves.
While Karsa is not as much of one now as he was when the series started, he's still quite fond of, and skilled at, combat. He also wants to end civilazation as it is and has no compunctions about the bloodshed he will cause.
We don't see Fener in action onscreen, but conversations about him suggest that he is rather irritable and fond of bloodshed. And of course, you know, the god of war.
The Seguleh form an entire nation of masked, battle-crazy warriors. That said nation only sent three people as their force against an entire empire is a testament to their prowess.
Bad Tom of The Traitor Son Cycle got his nickname precisely because he's a combat monster who loves being in the thick of the fight. He even passes the sizeable family fortune over to his younger brother because it'd keep him at home rather than out in the field with the Red Company.