Fallout: New Vegas has Father Elijah, the insane former leader of the Mojave Brotherhood of Steel chapter. Following a disastrous military defeat that saw the chapter driven into exile and terminal decline, Elijah sets out to unearth lost pre-war technologies he can use to bring about the Brotherhood's revival, alongside massacring the competitors who brought about their downfall in the first place. His pursuit of these technologies lead him to first begin fitting people with explosive collars to make them do his bidding, whom he kills once their use runs out, and finally to Attempt genocide.
The Courier can also be played like this (and pretty much every other way), if one wishes. Particularly if he goes the Wild Card route and maintains neutral karma, The Courier runs around the Mojave making alliances when it furthers his goals, removing factions when it furthers his goals, and generally doing whatever it takes to string the NCR, House, and Caesar's Legion along until he realizes his goal of a free (and quite likely, chaotic) Mojave.
The Renegade option in the Mass Effect series, particularly Mass Effect 2 (when it doesn't involve just being a dick to random shopkeepers).
The Illusive Man is willing to do anything if it will give Cerberus—and by extension, humanity—an advantage over the alien races and the Reapers.
The same goes for Aria, the crime boss of Omega. She knows who Shepard is but still cooperates when they both want the same people gone. When talking to her how her jobs can be done, she really doesn't care. Just do anything it takes to get the result.
Javik in the third game, as the avatar of vengeance, literally has no other purpose to live, other than to stop the Reapers. Throughout the game, he advises Shepard that nothing other than stopping the Reapers matters, and states as bluntly as possible to ignore, subjugate or destroy whoever is unwilling to help the war effort. For him, nothing is too precious to sacrifice against the unfeeling, eternal threat of synthetics.
According to the video archives of the Citadel DLC of the third game, the first Spectre was a Salarian operative who used 30 civilians as bait to flush out a target of his. Evidently this attitude impressed the Council enough to give him a job.
A literal example from the Dominions series: there is a certain creature one can summon called The Eater of the Dead. Should the player allow it to consume too many bodies, it will break from one's control, becoming the Unfettered.
In Planescape: Torment, the Practical Incarnation is this. He can and will do anything to find out the truth about himself and his own power. This effect is either slightly lessened when you realize his willingness to sacrifice his own life is due to his quasi-immortality, or slightly increased when you realize he will die to achieve his goals and even that won't stop him.
Havik from Mortal Kombat. Casting off primitive ideas like "measure" and "focus" gave him a real sense of measure and focus towards destroying the ideas of measure and focus.
Although it is part of Havik's Back Story that he was once The Fettered himself, utterly dedicated to order and peace; It took years for the priests of chaos to break his spirit, but once he freed himself from the shackles of reason and temperance he never looked back.
Raiden, once the civil and sage protector of Earthrealm, descends into this during the events of Mortal Kombat: Deception, having used the power of his godly essence to try to eliminate Onaga when he was released. Reconstituting as a more vengeful and angry god, he decides he won't stand for Earthrealm's wasteful handling of their own destiny and sets out to correct this by force. While this version of Raiden ended up erased thanks to the events of Mortal Kombat 9, the Raiden of the present timeline has also succumbed to such ways of thinking thanks to the events of Mortal Kombat X, where he is forced to draw out the evil energy pumped into the Jinsei by Shinnok. While he saves Earthrealm, the consequence is his sense of humanity and mercy towards others is compromised to nothing.
Tales of Berseria gives us Velvet, who only wants to murder Shepherd Artorias. To that end, she thinks nothing of starting a violent prison riot, colluding with thieves and pirates, or firebombing an entire port (and cratering the town's economy) to steal a single ship. Oh, and she's the protagonist. The fact killing Artorias and dismantling the Abbey on the way to him is good for the world in the long run is genuinely a complete accident.
Chrono Trigger: Magus does whatever it takes to destroy Lavos and save his sister, including leading the fiends in a war against humanity, learning dark magic, posing as an oracle to his own people, and even joining the heroes' party.
[PROTOTYPE]: Alex Mercer is a wild example of an Unfettered that gets Fettered. He starts out totally without rules, only with hunger and hate... and slowly picks up Fetters. Doing so makes him much, much stronger.
Blackwatch, on the other hand, never had any fetters. They're perfectly willing to firebomb entire city blocks to wipe out The Virus, and some of them actually enjoy doing so.
The ex-Death Knight, Thassarian, is very close to this in World of Warcraft Wrath of the Lich King. As one of the first Death Knights raised into the Scourge army, he has a long history of reasons he wants to pay Arthas back. As far as he is concerned, revenge is the only option or consideration.
After the victory against Arthas in Wrath of The Lich King, players can encounter Thassarian again, this time fighing against the Horde; he says that after his revenge, all he has left is war.
God of War: Kratos is one of this trope's more violent examples. Absolutely nothing will stand in the way of his goal, which is no less than the destruction of Zeus. Even if it means cutting his way through the rest of the Greek Pantheon. His only moment since his family's death of being fettered came just before Pandora's Heroic Sacrifice.
Knights of the Old Republic: Revan is a zig-zaggy example. He started out as The Fettered (he was a Jedi, after all), slowly lost his fetters as he fought in the war, became a Sith, became The Unfettered, toughened up the galaxy by beating several distinct shades of hell out of it, lost his memory, became a Jedi again, went Light Side, and became The Fettered once more. In canon, anyway. You can play him as The Unfettered all the way to the end, if you really want, and the Dark Side ending is him picking up right where he left off, preparing the galaxy for invasion from the Sith Empire, which makes for much less zig-zagging.
And then comes Star Wars: The Old Republic where after spending three hundred years a prisoner of the Sith Emperor, he becomes completely determined to wipe out all traces of Sith DNA in the galaxy. Which includes 97.8% of the Imperial population.
Red Dead Redemption: John Marston, outlaw turned rancher turned reluctant frontier government assassin, does absolutely everything to get his family back, up to and including helping overthrow a tyrant during the Mexican Revolution to install an even worse tyrant. While he's certainly polite and has some moral standards (up tothe player), his quest to get his old life back, and the lengths he has to go to, mean he'll stop at nothing to get his family back.
Max Payne: "Collecting evidence had gotten old a few hundred bullets back. I was already so far beyond the point of no return I couldn't remember what it had looked like when I had passed it."
Modern Warfare 2: A man has been locked up in a gulag for five years. His first act upon getting out? Lead a commando raid on a Russian nuclear missile sub base to fire a nuke at the US Eastern Seaboard to both garner sympathy for the US and to use the EMP to knock out all the Russian equipment and halt the invasion. Because after five years in hell, your mind begins to snap a bit. Or, in his view, your eyes begin to open to possibilities you wouldn't have considered before, and you'll do whatever it takes to win. Gentlemen, this is what happens to Captain John Price.
Similarly, Samurai Warriors gives us Nobunaga Oda, depicted as ruthless and willing to do practically anything for his goals. Buck the social trends of the era and promote officers based on talent? Plot treachery with a neighboring lord's retainers to pull off a backstab when it's least expected? Burn down an entire village and massacre its civilians and religious followers because their militia opposed him? If it accomplishes his aims, he'll do it.
Finally, Warriors Orochi gives us Orochi himself...no remorse, no hesitation, no qualms about doing anything to have fun with the humans he's captured for a Massively Multiplayer Crossover. He expects to be futilely opposed by his enemies and unconditionally obeyed by his subordinates, and that's about all he wants. He goes as far as to casually decapitate one of his longest-serving officers just for questioning his orders once.
The protagonist of NieR is a man determined to save his (depending on the versions of the game) sister / daughter Yonah at all costs and does not hesitate to destroy those who get in his way, ultimately destroying humanity itself in his journey.
"I swore to protect my daughter and my friends. If someone puts them in danger, they must stand aside or be cut down!"
Prince Bhelen of Origins is an utterly unscrupulous and ruthlessly powerhungry politician whose only concern is to become King by any means necessary. However, once he does achieve power it's shown that rather than a maniacal Caligula, Bhelen is a belevolent dictator who makes progressive changes to dwarven society (mostly involving giving the lower class dwarves more rights), opens up trade with the outside world and wins back territory from the Darkspawn due to allowing the casteless into the army.
Dragon Age II reveals that after becoming King, Bhelen apparently arranged the assassinations of each and every one of Harrowmont's family members down to only a single male who ends up fleeing to the Free Marches, giving up his position in dwarven society in the process. Going that far ensure his position and avoid reprisal doesn't seem like a terribly fettered thing to do.
The basic idea of the Grey Wardens is that they can go to any lengths—conscripting murderers and criminals, sacrificing cities, leaving armies to a horrible fate, and sacrificing their own lives and the lives of everyone they've ever cared about—in order to defeat the Blight. This is most clearly, and horrifically, shown in Dragon Age: Inquisition, when Corypheus manipulates them into thinking that The Calling is coming for every Warden, frightening them into wanting to stop future Blights as soon as possible, leading to them committing atrocities such as Human Sacrifice, in order to summon a demon army to help them kill the last two Old Gods before they're all gone.
Anders develops into this as Dragon Age II continues. In Act 2, he can be driven to murder by his little friend, and views this as his worst deed ever, bringing up again and again how guilty he feels about it. In Act 3, the demon starts winning, pushing him more and more into fanaticism, and he ultimately blows up the Chantry to force a confrontation between the mages and the Templars.
The entire dwarven race is this in Armageddon MUD. Every dwarf develops an immensely difficult goal as they reach adulthood, and they will not stop at anything to attain said goal. Reaching their chosen focus only leads to the dwarf finding another, often even more difficult goal.
In Shadowverse, Eleanor cares only for research and not the upcoming war.
Durandal from Marathon goes Rampant and begins messing shit up apparently for giggles (typical of the "Anger" stage of Rampancy), but when he calms down, he becomes this: his single goal being prolonging his existence. Anything bad that might happen to the human race is irrelevant. Anything good that might happen to the human race is irrelevant. Durandal's morality pretty much boils down to "If it's useful, make use of it; if it's useless, ignore it; if it's a threat, kill it." The only reason he more or less "sides" with the player in the games is because the Pfhor are a greater threat to him than humanity is, and the player is "very good at killing things."
Zoran Lazarevic of Uncharted 2: Among Thieves believes that the lack of mercy and compassion in pursuing one's goal is what makes one strong, citing men such as Hitler and Pol Pot as examples. By the end of the game, he considers NathanDrakethe same.
Liir Black Swimmers from Sword of the Stars have as a goal 'protect their fellow Liir from aggression'. Since they've already broken the greatest taboo of the Liir—being willing to inflict harm on others—any question of 'restraint' in terms of method is hypocrisy to their eyes. A Black Swimmer sees no distinction between firing a warning shot or exterminating another species by infecting their worlds with deadly viral bombs—both are merely means towards the end.
Arthas in the human campaign of Warcraft III becomes this more and more as the campaign goes on, not caring what he has to sacrifice if he only can kill Mal'Ganis. It didn't end well.
In Metal Gear Rising: Revengeance, the Big Bad believes everyone in the United States should be unfettered. He wants to give the people true freedom, the right to determine morality for themselves and to fight for their own causes instead of for money and others' causes. Raiden agrees with him to a certain extent, but still believes he's batshit insane.
Raiden himself slips into this. Over the course of the game, he leaves his family, his job, breaks laws, cuts through a little boy to get at the evil scientist holding him and other kids hostage, and gives into his own bloodlust. When the Big Bad claims that they would both do anything to get their way, Raiden doesn't really disagree and the epilogue reveals that by leaving Maverick to "fight his own wars", he's become the embodiment of Armstrong's ideals.
The Batter, the stoic protagonist of Off, is on a mission to purify the world, and he will see that it's accomplished. This means killing his supposed wife and creator, and, if you choose his ending, throwing a switch that eliminates the entire world, including himself.
Quite a few examples from Armored Core fit this trope perfectly—most distinctly, Thermidor/Otsdarva from For Answer, who is willing to commit mass-scale terrorist attacks, form and break alliances in an instant, abandon his own men and massacre billions in order to give mankind a chance to expand into space.
Annarotta Stohls from Super Robot Wars Z3: Jigoku-Hen is ruthlessly violent when it comes to fulfilling her mission, and won't refrain from pulling inhumanly cruel moves on her opponents.
Colress of Pokémon Black 2 and White 2 will, by his own admission, do anything to advance his research into the hidden potential of Pokémon. He allies himself with Team Plasma in pursuit of this goal, but ultimately acknowledges the merit of the protagonist's methods.
"If it means the strength must be brought out by the interactions between Pokémon and Trainers, then so be it! If it means you have to use a merciless approach, like Team Plasma's, and force out all of the Pokémon's power, then so be it! And yes, if the entire world is destroyed as a result, then so be it..."
In Civilization: Beyond Earth's Rising Tide expansion, the Supremacy/Harmony hybrid affinity is described by the developers as "power by any means", using both extensive cybernetics and genetic modification to turn their citizens into things that just aren't recognisably human any more.
"I don't care who I have to hurt. No one else matters. Sempai will be mine. He doesn't have a choice."
The Jennerit from Battleborn in general are this as they'll do anything at any cost in order to achieve their goals. This is so much so that their culture's official motto is: "Any Deed. Any Price."
Borderlands 2: Handsome Jack will do, quite literally, anything to remake Pandora in his image - sacrifice countless resources to destroy the Vault Hunters, spend a fortune on an Egopolis, trap his daughter in a jar for her entire life...
Alien Syndrome (2007): Final boss Isadora Midas was forced into eternal life and desired to die. The killer she picked out for herself was Aileen Harding on account of the similarity between the two of them. However, believing that Aileen would never kill a child, she forced the other's hand by destroying many ships and stations, killing or grossly mutating its inhabitants, including Aileen's fiancé, and threatening to continue her actions would Aileen not stop her.
This is a cultural trait of the Sload, a race of "slugmen" native to the archipelago of Thras to the southwest of Tamriel. The Sload are a race of careful and deliberate Chessmasters who are utterly ruthless in the pursuit of their goals, with even genocide being on the table if it helps them achieve their ends (though a reluctant option after their last major try, in the First Era, backfired severely). Making matters worse, they are naturally skilled at necromancy and mysticism (especially the capturing of souls), leading them down some extremely dark paths. While they tend to operate on their own Blue and Orange Morality, they are universally seen as Always Chaotic Evil by the other races of Tamriel. (Attempting a Final Solution using a Mystical Plague which killed half the population of Tamriel will tend to cause that...)
In League of Legends, most of the Noxian leadership believes that you should do whatever it takes to win. This has created a bit of a conflict with the more Social Darwinist side - one champion, Riven, is a Defector from Decadence after they deployed chemical weaponry to destroy both her regiment and a Demacian one, rather than allowing them to fight it out and see who was stronger. There are also individual characters from outside Noxus who slip over into this trope, such as Xerath, who at one point brought about the destruction of his home country in order to attain his personal freedom, and centuries chained in a pit hasn't exactly made him less fixated.
Mystery Case Files gave us Alistair Dalimar, who devoted his entire life solely into the search for immortality. He spent more than five hundred years seeking it, and nigh everything he ever did was driven by this goal. His quest led him among others to search for an Ancient Artifact on the entire globe, conduct some a wide number of gruesome experiments, brainwash and even kill many innocents, sink his own hometown into the sea, and kill his very own offspring (at the very least his daughter Lily and his granddaughter Gwendolyn) - it was even hinted that he had children solely to use them as pawns in his plans in the first place.
All of the playable characters from Detroit: Become Human can be this, depending on the player's choices, but a special note goes to Connor. Most of his story focuses around his mission: to investigate and stop the spread of android deviancy. He can prioritize this mission over saving his partner Hank from potentially fatal situations (or outright kill him), he can kill an innocent android for his creator's amusement in exchange for information, and when he and Hank are taken off the case, Connor will go behind the police's back and investigate on his own. Thanks to his Body Backup Drive, not even death will stop him, and later, once the US calls for the immediate recall and disposal of all androids, he can commit suicide to avoid a conflict and come back later. Even in an ending where the androids win their freedom and convince the world that Androids Are People, Too, Connor can defy everyone else and assassinate the android leader.
The Sly Cooper games have two (actually three) well-known examples.
Arpeggio in Sly 2: Band of Thieves resented other birds for being able to fly while he can't, triggering his main motivation to seek out and reconstruct Clockwerk, the original Big Bad, and merge with him in order to fly and become immortal through The Power of Hate. He sends his protégé, Neyla, out to aid the Cooper Gang in retrieving the parts from the other members of the Klaww Gang so she could steal them later on for delivery. But in the end, Arpeggio had no idea that Neyla herself was an unfettered, too, and had other plans with Clockwerk; the moment he's ready for the merger, Neyla wastes no time in betraying her boss and killing him as Clock-La.
Penelope in Sly Cooper: Thieves in Time was just as determined as Arpeggio, and just as selfish as Neyla. Her goal was to accumulate billions of dollars through weapon dealings in the black market, and then Take Over the World. But she needed Bentley's cooperation to get that far, and he's more interested in robbing other villains with his Childhood Friends due to a strong sense of honor, so she attempts to kill them both, which backfires. When Bentley tries to call Penelope out for this, she tells him their relationship is off and attacks him, showing wealth and world domination mean more to her than love. The game ends with her remaining deviant on her goals, including a newfound desire to murder her ex-boyfriend.
In Fire Emblem: Three Houses, Edelgard proves throughout the game that nothing is beneath her in her quest to destroy the Church of Seiros. Her actions in pursuit of this goal include having the heirs apparent to the continent's other nations assassinated (one of whom is her childhood friend and first love), teaming up with sociopaths who burn down villages For Science!, betraying her classmates and teacher, and physically warping her body into a demonic form in order to combat her enemies. If Byleth chooses her and stays with her, they act as a Morality Chain, but otherwise all bets are off.