Most of the Ace Combat games turn you into this during the course of the story. It is quite awesome to hear other pilots on the radio shit their pants when they learn you've entered the battlefield.
Most notably in the fifth game of the series; the protagonists become so feared by the enemy they are given the nickname "Razgriz" (after a mythical demon with a penchant for leaving death and destruction in his wake) and the mere mention of them is enough to cripple morale.
Terrified Yuktobanian Soldier: Help us! It's the Razgriz!
This is how the Karma Meter works in Medieval: Total War, with a Chivalry-Dread axis. Generals earn Dread points by fighting dishonorably, executing prisoners of war, or exterminating the populations of captured cities. On the strategic map such characters will reduce a settlement's growth and tax income, but increase public order. On the battlefield Dreaded generals reduce the morale of opposing forces, and a sufficiently infamous general can cause entire armies to rout simply by charging. These characters often pick up appellations such as "the Tyrant," "the Wrathful," or "the Merciless."
Joel is The Dreaded throughout much of The Last of Us whether it's in the Boston Quarantine Zone, Pittsburgh, or Utah. In the Boston QZ he is feared as a dangerous smuggler with plenty of connections, in Pittsburgh he is simply the 'Man in the Truck' who mercilessly slaughtered patrol after patrol leaving no survivors, and among the Cannibals he is known as the crazy college man. This gets to the point where the cannibals are actively running away from him in a fight. Ellie also earns the status of The Dreaded among the Cannibals for her bloody escape from the college and the Roaring Rampage of Revenge she goes on in their town later on.
Someone in Fable or its sequel who is both famous and evil will cause non-combatants to run at the sight of you. Particularly if you start attacking, or if you've just been for a bit of town-burning previously. You'll never be totally feared though, some brave (and foolish) soul will summon up the courage to call you out on your crimes, and the guards will always do their best even when its a lost cause.
By the midway point of Far Cry 3, Jason has gone from being a kid at the wrong place and wrong time to making pirates soil themselves at the mere mention of Snow White.
In Far Cry: Instincts, the XBox360 version of the original game, for a while you become the monster movie monster, the creature lurking in the dark that messily kills people one by one.
Giygas of EarthBound is a physical manifestation of people's fear.
Dot Hack GU: Haseo, the hero, is nicknamed "The Terror of Death". Most Player Killers he runs into throughout the game will invariably be terrified at the sight of him, and even some random normal players will react in fear upon passing him in the streets. It doesn't help that he styles his usual look after The Grim Reaper and wields a massive Sinister Scythe as his weapon of choice.
Joker: Now, don't worry, boys. I'm sure there's no truth to the rumors that Batman drinks human blood.
Similarly, in Armored Core games, the player starts out as a relatively unknown rookie, before quickly working himself up in the ladder and becoming a renowned and feared pilot, usually to the point where the local The Chessmaster decides they are too dangerous to leave alone and tries to eliminate them, usually by ambushing them with multiple high ranking AC pilots.
The phrase "It's Lu Bu!" strikes fear into even the mightiest player! And every other general on the field... "Do not pursue Lu Bu" indeed.
Lu Bu's erstwhile subordinate Zhang Liao gets this reputation among the forces of Wu, where his appearance causes the armies of Wu to flee in terror at He Fei.
Shu's Guan Yu is so feared that it takes a combined strategy between Wu and Wei specifically to kill him.
Final Fantasy VI: Emperor Gestahl's around? No problemo. General Leo? He's a cool guy. Kefka's here!? Oh Crap!. It gets more pronounced as the game goes on, too.
In Final Fantasy VII, Sephiroth is spoken of with a combination of hate, reverence, and fear; the suggestion of his presence is enough to cue an Oh Crap! from the heroic characters, especially Cloud, who knows him best.
Final Fantasy X: Sin is dreaded all around Spira. It's huge, insanely powerful and solely bent on causing destruction wherever it goes. It's also near-indestructible, as most people believe that only a summoner's Final Aeon can kill it; and even then, it always comes back, eventually.
in Warframe, the Grustrag Three are so intimidating for their sheer power and efficiency in capturing Tenno that the Lotus will immediately abort the mission you're on and demand you get to extraction ASAP before they are able to lay their hands on you.
The title character can become this, depending on player actions. If her body count increases rapidly, then both Tasen and Komato logs reveal many of their soldiers to be pants-wettingly terrified of the implacable "human anomaly" that's been tearing a bloody swath through everything they throw at her. Even if Iji's on a Pacifist Run she still scares the hell out of everyone on the field, partially because she's somehow able to make her way through a warzone without killing anything, and partially because she's collected so much ammunition that they're worried she'll become a miniature black hole.
Annihilators are so feared by the Tasen that one Tasen Soldier writes in a logbook that if they ever face one in battle, they're just going to lie back and hope for a quick death. And even by those standards Iosa The Invincible is regarded as such a terrifying death machine that after Iji kills her several Komato logbooks say that they're glad she's gone.
The Master Chief is referred to as "the Demon" by the Covenant. You get that kind of reputation after massacring thousands of Covenant troops and utterly destroying Halo, a sacred and seemingly indestructible installation built by their gods.
The other SPARTANs are also referred to as "Demons".
The Primordial/Captive/Precursor/Gravemind, he's not really a publicly known figure, but to those who do know what it is, the revelation that it's loose inspires shock and fear.
Pyramid Head is this to the other monsters in Silent Hill 2. It's so bad that if James equips PH's Great Knife, turns off his flashlight and drags it along, the signature scraping sound will cause enemies to flee.
Luca Blight from Suikoden II, a genuinely terrifying combination of Ax-Crazy and One-Man Army. To the point that even his own kingdom fears him and hardened warriors such as Viktor and Flik, who in the previous game faced down an Eldritch Abomination, don't even consider battling him unless they have an entire army on their side.
Assassin's Creed I: Alta´r is implied to be viewed this way in general, but it's definitely shown how much he freaks some of his targets out the further you progress into the game, to the point where one of them is so paranoid that he brutally slaughters a defenceless, elderly scholar simply because the man is dressed in white.
Ezio's reputation as this is Played for Laughs with Duccio de Luca, who is on the receiving end of a beat-down from Ezio in II and Brotherhood, due to cheating on his sister in the former and a foolish attempt to get even in the latter. By the time of Revelations, when he realises that Ezio is standing behind him when he's flirting with Sofia, he simply screams and runs in terror.
Samara, as well as all asari justicars, are famous for their relentless pursuit of justice and their brutal methods in doling it out. When Samara appears on Illium in pursuit of a particular criminal, the police force finds itself on edge, worried that she'd very easily turn on them if they tried to detain her.
Shepard themselves comes off as this to the Reapers. By the end of the second game, the Reapers are forced to admit that Shepard is actually a hindrance to their plans, the first and only time they ever admit such a thing ("Shepard. You have become an annoyance."), and in the third game every Reaper has top-priority "Kill On Sight" orders for Shepard personally, even turning their guns away from fleets in orbit, to kill this one human. In the LeviathanDLC, the Leviathans state that Shepard is the first thing in history (a history stretching back over a billion years, mind you) that the Reapers have ever feared. In the Twitter feed tie-in for Mass Effect 3, while the Reapers have dismissed all opposition with a tone of casual indifference, during their invasion of Earth a priority is issued for confirmation that "Hostile Target Shepard" is dead. When none comes, the Reapers actually get worried about the possibility that s/he's still alive.
This extends to a lesser (though still major) opponent: Cerberus. When Shepard arrives at the Alliance base on Mars during the prologue and finds that Cerberus has arrived and taken it over, the first reaction of the Cerberus troops when Shepard opens fire is essentially "Holy shit! It's Shepard!!" Worth noting is that these Cerberus troops are indoctrinated and partially turned into Husks - they're physically unable to feel fear, and they still panic when Shepard arrives.
Played for Laughs in the Citadel DLC, for a good part of the Normandy crew, when they all rush to the archives to find who is behind the attempted assassinations on Shepard. The CAT6 mercs are terrified of facing the entire team.
CAT6 merc: I think that turian they've got is Archangel! How the hell are we supposed to kill him?! Garrus: *BANG* You're not. —- CAT6 merc: But they've got a krogan! Why don't we have a krogan? Wrex: Wouldn't want to be you, princesses! HAHAHA! —- CAT6 merc: Shit! That's a Prothean over there! Javik: And that's a future corpse over there!
Everyone from senior Jedi to Mandalorians to Sith are intimidated by the name Revan. When your party hits the Star Forge, Malak panics and sends out every war droid and cannon fodder troops he can muster - not to defeat you, Revan, but just to slow you down while he prepares for a one on one saber brawl.
Likewise, many a flashpoint party in Star Wars: The Old Republic was torn between cheering and panic when they heard the words "Statement: Hello, Meatbags!" Yes, HK-47 is 300 years old. Yes, the droid will still kick your shebs. Imperial players also had this reaction to having to put Revan himself down like a rabid dog after Revan went insane and started planning genocide against anyone with a trace of Sith species ancestry.
Tol Braga: He's more than darkness; he is... a void...
The Aptly-named Dread Masters are the personification of this trope. Six powerful Sith whose combined strength can drive whole fleets mad. They have no compunction to use their powers to terrorize both Friend and Foe. In a way, they even fear themselves; they can only fully control their powers because they had to use the Force to create a sort of Hive Mind, so that they can share the effects of their powers equally between each other. After one of them dies, the Sanity Slippage starts going into full effect.
The Sith Warrior often gets this reaction from others due to the fact that you're more or less treated as a force of nature by your targets. A Light-sided Warrior can occasionally use their reputation to terrify their enemies into submission or retreat rather than killing them.
In Yggdra Unison, most people who are not Bronquian or didn't serve alongside Gulcasa at some point are scared shitless of him—and this reaction is fairly well-deserved. Being Unison, this is Played for Laughs—most notably in how Pamela tries to turn tail and run every time they meet, even when she's the one invading his land.
Hawke in Dragon Age II, to a lesser degree, as the enemies are usually smaller groups that Hawke slaughters before they have a chance to shit themselves, but the Arishok certainly fears Hawke enough that the first move of his attempted conquest of Kirkwall is trying to neutralise him/her. An odd example too, since in Qunari culture fear and respect often go hand in hand.
In the third act, Meredith's dialogue implies that she knows that Merrill and Anders are illegal Mages. Because of their friendship with Hawke however, she states that the only thing protecting them from the Templars is because she knows doing so, would end up bring a wrathful Hawke down upon her head.
In the ending, if sided with the mages, Hawke's Death Glare manages to make Knight-captain Cullen literally jump back, allowing Hawke and Co to casually leave the scene, despite being surrounded by Templars.
The Horsemen of the Apocalypse scare everyone. Heaven, Hell, and even their own superiors fear and respect their terrible power. The entire plot of the game takes place because nobody wants to cross all four of the Horsemen. In-game when Mooks encounter War their reaction is basically a Mass "Oh, Crap!" while they desperately charge you.
Both subverted and played straight in Darksiders II: many NPCs state the only reason they are not running away in fear of being on the same planet as Death is that 95% of his power is sealed.
Bowser of Super Mario Bros. scares everyone in the Mushroom Kingdom who isn't named Mario, Luigi, or Peach. In Super Mario RPG Bowser's presence in the party actually frightens away his former Mooks who have defected to Smithy. Yes, his mooks fear him more than they fear the living weapons factory from beyond the stars. It should be noted that Bowser is always portrayed as a Benevolent Boss, and his mooks are still scared of him.
By the time of Half-Life 2, the feats of GordonFreeman in the first game have been told and retold to such an extent that most of the planet is either in awe of him or intensely fears him, to the point where a mere glimpse of him in City 17 is enough to put the Combine on high alert.
Alma is generally considered to be the most terrifying thing in the game, both in and out of universe. The mere possibility of her being released and what this would mean results in total pants-browning terror to Armacham's personnel, to the point that Genevieve Aristide is willing to effectively detonate a nuclear-scale explosive in the middle of a major city to stop her. Eventually, the Point Man does the same. It doesn't even slow her down.
In the third game, there's The Creep. How bad is he? Alma is afraid of him. ALMA. For a good reason, too. It is the personification of the worst traits of her father, Harlan Wade. It turns out that the only way to stop it is for the Point Man and Fettel to actually destroy their own horrific memories of Harlan Wade when they were children so they can face the Creep and kill it.
By the later parts of the games, the Point Man, Fettel, and Michael Beckett become these to the ATC troops and even the Replica. They know that they can't stop these superpowered soldiers, and that fact scares the piss out of them. In the third game, the Phase Commanders have to order their troops to fight on pain of dismemberment to keep them shooting at Fettel and the Point Man.
Play right and get the right perk(s), and your character can become this for any one (or more) of the warring factions. The easiest group to do this with is the Powder Gangers when you attain the Vilified Status, when one of them refers to you their personal "GrimFuckingReaper."
Joshua Graham was this for the NCR and is now this for the Legion, who speak of him as a vengeful spirit (they're not completely wrong). NCR snipers made no less than 5 attempts on his life, all of which failed despite all of them managing to shoot him and after his failure to take Hoover Dam Caesar had him covered in Pitch, set alight and thrown into the Grand Canyon. Even that wasn't enough to put him down.
Graham's successor Legate Lanius is equally feared as "The Monster of the East", with the Lonesome Road DLC stating that his greatest weapon isn't his skill in combat (though it is indeed formidable), but his carefully cultivated reputation as a mythological figure feared by both his enemies and his own men.
Father Elijah, by virtue of being bat shit insane and the greatest mind the Brotherhood of Steel has ever seen. When he got to Big Mountain he managed to hijack two of the think tank professors (two of the greatest minds of the 21st century in robot jars) and is regarded as their most dangerous criminal. Christine Royce, charged with hunting him down, is more than a little wary of him and tries to keep as much distance between them when trying to kill him. It doesn't work out.
The Think Tank in Old World Blues are not only talked up as terrifying opponents by Dr. Mobius, they are so dreaded that they even scare Ulysses, the Big Bad of all four DLC. In one log, he states that it would take a hundred Elijahs to challenge them. They've got cheat codes, and if you manage to bypass the Pacification Field, they're not actually that tough.
Randall Dean Clark of Honest Hearts was an old Pre-War soldier who became a Crazy Survivalist after entering Zion National Park. He was eventually joined by some Spanish-speaking refugees, and he began secretly providing them aid and supplies. When an expedition from Vault 22 butchered the refugees, Clark began a one-man guerilla war against the expedition. After methodically wiping out two-thirds of the hundred-strong group with traps, explosives and his trusty custom rifle over the course of almost a year, the survivors began to attribute the deaths to an evil spirit which haunted the canyon, and fled in terror, but not before leaving thisApocalyptic Log. Randall eventually took under his wing a group of children whose ancestors would go on to become The Sorrows tribe.
The Dragonborn in The Elder Scrolls V: Skyrim is one to the Dragons, being a mortal who has all of their powers and the ability to devour their souls. Listen carefully during your first fight with one and you can hear it realise who it's dealing with. Considering they take half-damage from anything that isn't you, it's pretty justified. The soundtrack during Dragon-fights is even titled "The One They Fear".
The Dwemer (Dwarves) were feared by the Nords, the Chimer and even the gods themselves. They were ruthless Abusive Precursors who viewed everyone who wasn't them as guinea pigs for their mad science experiments, known for intentionally summoning demons to test their divinity and eventually possibly wiping themselves out by tinkering with the heart of a god.
The CEO/Mob Boss "Drake" in the SNES Shadowrun title. Much of his mystique comes from no one seeing his face. In what will come as a surprise to no one who's played the tabletop game, he's actually a dragon; in a cyberpunk future, their trademark Money Fetish manifests itself by becoming captains of industry.
Downplayed with Valvatorez. He is actually a very nice fellow to be around. Justified in the fact that he REALLY IS powerful enough to warrant that reputation. Infinitely more so in his Tyrant state.
Sepulchure in Artix Entertainment games fits this trope really well. In fact, anyone who isn't the hero or any of his/her allies or even King Alteon himself, or doesn't affilate with the Shadowscythe in any way is afraid of him. Even some of the Pactagonal Knights are scared shitless of him and his flying dracolich fortress of Shadowfall.
Diablo himself; appropriate, given that he's the Lord of Terror.
In Diablo III the Nephalem becomes this for enemy forces. You find a journal from a cultist who is dreading his current assignment of being part of the scout party looking for you.
BioShock has Frank Fontaine, the Bronx mobster and smuggler who ran Rapture's underworld and Plasmid market. Among those who knew him, his reputation for ruthlessness was such that half of the city are "still jumping at his shadow" nearly two years after his death has been widely publicized. At one point, the player comes across an audio diary on the electrocuted corpse of a thug who was interrogated for information on Fontaine by Andrew Ryan's men. His response is "Fontaine can do double!" One of his employees Dr. Suchong, however, remarks that although Fontaine "is scary son-of-a-bitch" and has styled himself into the Boogeyman of Rapture, he prefers his employment over that of the "cheap son-of-a-bitch" Ryan. This is in part because he reasons earlier that, underneath all the "flim-flam and humbug", Fontaine is just another con-man. Fontaine's main advantage is that he's in a city of artists and intellectuals, not hardened killers.
The Spy fulfills this role amongst the enemy team. A lot of the meta-game is about identifying, finding, and killing enemy Spies before they can cause chaos. A common complaint in game? "Man, I hate good spies!"
And then it loops back around due to Spies generally being terrified by Pyros, who are the natural counter to Spies and the usual lot who check for them behind their team's lines. Even fully-cloaked Spies give Pyros a wide berth, as even a split-second puff of flame from a trigger-fingered Pyro who thinks they saw something can make your death a certain thing. "Meet the Pyro" reveals that, in canon, the fear of the Pyro extends to everyone - including his own teammates. He sees a Sugar Bowl where he dances around, sprays rainbows and bubbles around and gives giant lollipops to fat cherubs. His enemies (what the cherubs really are) see a faceless monster who burns anyone he runs into and chops up the survivors with his axe.
Heavy: I fear no man. But that... thing... it scares me. Scout: No, I- I ain't talking about that freak, alright? *beat* He's not here, is she? (panicking now) How do I get this f**kng thing off!? Spy: One shudders to imagine what inhuman thoughts lie behind that mask, what dreams of chronic and sustained cruelty...
Gameplay wise, being in the vicinity of the ghost on the Harvest Halloween event map is enough to make even the most hardened of mercenary scream and lose all will to fight. The Headless Horseless Horsemann also has a similar effect.
Interceptors are this in EYE Divine Cybermancy. Though easily destroyed with anti-tank weapons, their tendency to sneak up on players and their extremely powerful battle cannons (enough to kill most unshielded characters instantly) have given many players a well-justified paranoia in any areas they can spawn in.
There are several in RuneScape, but the crown has to go to Nex, whose mere presence terrified the gods enough to make them temporarily band together to seal it away.
This can be invoked by having your levels be high enough - underleveled enemies will flee from you on the map (until they hit a wall at least, at which point you can get a pre-emptive attack if you want).
Lucas gradually becomes regarded as this In-Universe by the villainous Pigmasks. The only one in their ranks to actually impede him was their Commander, the Masked Man; once Lucas overcomes this threat, all of the Pigmasks there to witness it run like hell.
Upon realising that the Ultimate Chimera is the last of the experiments from the Chimera Labs that had not yet been recaptured, a horrible silence falls around the Pigmasks who knew that they'd now have to try to contain it. The player is told several times NOT to engage it if they see it, and for good reason.
Wilhelm is stated to have been able to defeat the Vault Hunters of the first game, with Angel often fearing his intervention. When you finally encounter him, Roland immediately tells you to retreat. Despite this, he's an Anticlimax Boss that goes down easily. There's a reason for this: Jack wanted the Vault Hunters to defeat Wilhelm so they would loot the body, take the unusual power core that he was carrying, and link it to Sanctuary's shield genetators so that he could shut them down. In Borderlands: The Pre-Sequel!, in which Wilhelm is one of the playable characters, his backstory is that he was one of the greatest mercenaries of the galaxy and is a semi-legendary figure to those who recognize him.
All the Vault Hunters to some extent. They are walking apocalypses who can take whatever Pandora or Elpis throws at them — hostile wildlife, ten-foot-tall-robots, bandit armies, Private Military Contractors-you name it, they can drill it with bullets/whack it to death/blow it up and still survive to fight another day. And if they're working together, god help anyone who encounters them.
Dishonored gives us Corvo Attano, the player by the end of the game. Given that the entire game is his Roaring Rampage of Revenge, this is rather unsurprising. Depending on how you play, the Final Boss may end up killing himself out of sheer fear of what Corvo will do to him. Similarly, Corvo's Evil Counterpart and master assassin Daud is also feared as the "Knife of Dunwall".
The Reaper in Persona 3. Five words ("Be careful! I sense Death!") are enough to make both the party and the player collectively soil themselves.
Agent Forty-Seven of Hitman fame. If you hire him, you're always buying death - to be delivered swiftly upon your enemy with no evidence left behind. Other killers from the International Contract Agency are Properly Paranoid of 47, which shows best in the few levels of Absolutionwhere they are actively hunting him.
Prince of Persia: Warrior Within: The Dahaka is this to everyone in its path including the player. It cannot be reasoned with, it cannot be stopped, it is terrifying and it will kill you.
Iris Heart in Hyperdimension Neptunia Victory. Everyone - allies included - learns that you only take Plutia lightly once. The mere threat of her activating Super Mode is enough to make major villains rethink a confrontation, lest they require additional months of therapy.
Samus Aran becomes this to the Space Pirates during Metroid Prime trilogy. The pirates start panicking when they see Samus effortlessly storm their bases and defenses and they basically go Oh Crap! in Echoes when they discover that Samus and her dark copy, Dark Samus, are running around at the same time, killing them. All three of the Prime games have Apocalyptic Logs, and in the ones written by the Space Pirates, she's the apocalypse.
The SA-X serves this role in Metroid: Fusion, and with good reason - for 95% of the game, your only defence against it is hiding and/or running away when it is near. If it spots you, pray that you're able to dodge its attacks or you'll wind up staring at the game over screen very quickly.
Medivh from Warcraft. Whether it's because he was possessed by the most powerful Mad God in the setting or because of his own considerable magical power and knowledge (the very reason the Mad God was so eager to possess him), even other powerful beings would give him a wide berth. Gul'dan, Kil'jaeden, and Deathwing all feared Medivh. The only reason Anduin Lothar and his companions were able to kill Medivh was because Medivh had already exhausted most of his power fighting his mother Aegwynn. Decades after his supposed demise Medivh is still considered one of the worst threats to ever appear on Azeroth. When he came back to life to try and make up for some of the damage he had done previously, he had to conceal his identity so people he needed to work with wouldn't run screaming from his presence.
Trevor Phillips in Grand Theft Auto V is one of the most feared characters in the entire franchise, and almost certainly the most feared protagonist. Everyone who knows him, even his friends, speak about him in cautionary tones. Even his former best friend, Michael Townley/DeSanta, is terrified of him and describes him as "Hell walking on Earth."
Tomb Raider (2013): Lara Croft herself becomes this when she gets Tired of Running from the Solarii goons and decides to fight back. Over time, Enemy Chatter both in and out of combat reveals that the mercs are actually scared shitless of her and hope they don't run in to her. They don't even know her name, but they start uniformly referring to her as "The Outsider". Not an outsider. The Outsider.
Ghetsis has become this by the time of Pokemon Black And White 2, when the world at large is aware of who he is, what he's done and what he's willing to do in his quest for power.
Shu Shirakawa of Super Robot Wars fame has not only achieved this in-game, but has also achieved this on a meta-level with veterans of the game. Whenever he shows up, something bad is going to get worse. And this is before we mention NeoGranzon.
In City of Heroes player characters, both hero and villain, became this over time to enemies, at least reflected in the dialogue. More than a few enemies in missions would declare such statements as "I didn't sign on to fight *character*!" That said, it was also fairly easy for players to make this with their power choices - Dark Armor had a power that generated an aura that caused enemies caught in it to quake in fear, and anyone could get the Presence power pool, which capped off with the power "Invoke Panic". In the early days, enemies hit with Fear would immediately turn tail and run, further reinforcing this image. A high level player could wander into one of the random groups of low-level enemies (outside a mission) and would be ignored due to a game mechanic preventing low-level NPCs from pointlessly killing themselves by attacking players they had no hope of defeating, even en masse. If any one of the enemies was hit by some kind of power, however, the entire group would immediately flee.
Monster Hunter 3 Ultimate has the Deviljho, an Extreme Omnivore monster who starts appearing in High-Rank quests. The Guild Sweetheart warns you the first time you see it in a Moga quest, and in the "Everyone so Big-Big!" video, the hunter, Felyne, Melynx and Cha-Cha at the end all run for their lives as a Deviljho spots them, complete with the series' signature Scare Chord.
In Drakengard 3, Zero is openly feared by the mooks who face her, all of whom generally cower in fear and scream for their mothers as she cuts her way through them.
God Of War Series: Kratos is portrayed as being feared by nearly all of Greece, in part due to the various atrocities he committed while serving Ares. In the first game, several people are more scared of him than of the various monsters and beasts, with one person even flat-out telling Kratos to his face that he would rather die than be saved by him. Pandora even says outright in III that everyone who knows about Kratos is scared of him, to which Kratos simply remarks that "there are reasons for that."
[PROTOTYPE 2]: Alex Mercer has become this as of this game, and for good reason considering he's the cause of the Blacklight outbreak. In the game's beginning, Red Crown's reaction upon learning that Alex is in the Red Zone is a very panicked "Oh, shit!"
In Dark Souls I, most enemies are described as powerful, but beatable. The one exception is the Bonus Boss, the Black Dragon Kalameet. He is described as the sole remaining Everlasting Dragon, having survived the war that exterminated his species, and is so vicious that "even mighty Anor Londo dared not provoke his ire". Anor Londo is also known as the "City of the Gods" and was the civilization largely responsible for mass-slaughtering the Everlasting Dragons in the first place. And they are terrified of Kalameet.
Aforementioned vampire, Flandre Scarlet, is feared by main characters, her fellow Scarlet Mansion Cast Herd, even her own sister, who confined her to the mansion's basement in an attempt to protect everything from her. She has power to utterly annihilate anything unfortunate enough to be targeted be her, at one point casually vaporizing a meteor shower, and while she bears no malice to anyone she has poor impulse control.
Oni were exiled from Gensokyo some time ago for causing too much trouble and since largely disappeared, which is good since they're all have immense Super Strength and are absurdly resilient even by youkai standards, and they have a tendency to pick fights with everyone. The return of Suika Ibuki caused much consternation despite her being largely friendly, and it is to everyone's relief that Yuugi Hoshiguma has deigned to stay in Former Hell, given she's rumored to be able to collapse buildings with just her footsteps.
In Jurassic Park The Game, the mysterious predators that harass Nima at the beginning, later revealed to be Troodon, are feared by most other carnivores. During Episode One, Dilophosaurus run away when they hear its cries, and during Episode Two, flocks of Compsognathus flee from them in the Visitor Centre. Even the Velociraptors, the most feared dinosaurs in the broader franchise, won't go anywhere near their nests.
Springtrap, the new animatronic from the third game manages to be this even to the other animatronics.
League of Legends: Every character originating from the Void is one of these, but Rek'Sai is feared even by her fellow void creatures to such an extent that Vel'Koz and even Cho'Gath want nothing to do with her.
Seeing a large enemy army unit, shown as 3 men in a group, approaching your counties on the map, especially if you don't have a castle up yet, and/or your main army is too far to intercept them.
In battles, if the enemy takes up a very good defensive position where their archers can unleash their arrows on your forces while protected by their own forces. Expect to take massive losses if you don't have your own archers.
If the enemy has a large group of crossbowmen. Though they fire much slower than archers, and have a much shorter range, any hit from one of their bolts is guaranteed to make you lose 1 person per shot, even pikemen.
In Undertale there is none other than YOU, if you choose to kill every monster in your path. Eventually you start hitting "empty" Random Encounters and find that all the puzzles have been completed for you by all the monsters that are fleeing in sheer terror of the thing that is sweeping through and slaughtering everything it encounters. Even the final boss Asgore is scared and tries (very unsuccessfully) to talk his way out of a fight.