Godzilla has time and time again become this by somehow beating monsters that are even stronger, faster, or smarter than him, largely by virtue of being The Determinator. He's not (quite) the most powerful kaiju, but due to him overcoming seemingly impossible odds and almost invincible enemies, he has earned himself the title of King of The Monsters. He rarely loses, but when he does it's a shock for onlookers, to put it mildly. Virtually anyone who can fight with him on equal ground is seen as just as bad as him, and any who can beat him are seen as worse than a nuclear bomb going off. He's not the Trope Namer for the Godzilla Threshold for no reason.
Of special note is Godzilla vs. Destoroyah, where not only does Godzilla rise to the level of "super monster" himself, but his power is so out of control that when he dies his death threatens to release enough energy to light the planet on fire and melt through to the core of the Earth. And this is going on the same time as a new super monster, Destoroyah, shows up and proves it is equal in power to the now-super monster Godzilla (at least until his power rises when he is near meltdown). Keep in mind that his "Burning" form is already strong enough to easily dispatch most past monsters who gave him hell without even being near meltdown. Dread does not even begin to describe what G-Force is feeling when they have two super monsters who are super even to other super monsters along with The End of the World as We Know It to deal with all at once.
"Listen, kid. There are two things you don't know about the Earth. One is me, and the other is... Godzilla." The Xilian leader in Godzilla Final Wars quickly learns that Godzilla isn't something to be taken lightly.
Anytime the Mutos showed up in Godzilla (2014) , you can bet it was a scary moment. Even when they were just shown on the news, such as the female one running through Vegas, was pretty creepy. Little wonder that the military attempted to use nukes on them, albeit in a rather unconventional way.
The deliberatelymelodramatic opening crawl for the movies always refers to something as "dreaded" — the "dreaded Imperial Starfleet", the "first dreaded Death Star"...
Darth Vader in particular, who is a six-and-a-half-foot-tall, caped black knight with magical powers and super strength. He makes a triumphant entrance to the film's famous soundtrack, cape swirling, and lifts a captive soldier up and snaps his neck with one hand as an Establishing Character Moment. It just goes from there.
In the Expanded Universe Darth Vader is still viewed as an example of pure evil hundreds of years after his death. The man really left an impression on the Galaxy it would seem.
And Imperial officers, Vader included, used the Emperor's name to scare their co-workers.
Vader(to the commander of the second Death Star): ...the Emperor is not as forgiving as I am. (The commander of the second Death Star soils himself)
Boba Fett has this reputation, all the more impressive since he's a Badass Normal in a galaxy dominated by lightsaber-swinging sorcerers. Then again, it's well established that Mandalorians in general are folks you'd rather not get in a fight with.
The Agents in The Matrix serve as this, at least in the first one, where Morpheus advises Neo to simply run away if he sees one.
Ra's al Ghul is a name criminal elements know well, and when mob boss Falcone hear he's coming to Gotham, he reacts with terror.
Batman has cemented his status as this to Gotham's underworld by the beginning of The Dark Knight, to the point that the mob has been put wholly on the defensive within a mere year's time, and the mere sight of the Bat-Signal is enough to deter many from criminal activity.
The Joker in The Dark Knight is feared by the mob, the cops, and the politicians for being an Ax-CrazyMagnificent Bastard. Even at the beginning of the film, his own goons are telling each other legends about him.
Bane in The Dark Knight Rises, he has already got the overthrowing of a small country to his name prior to the movie, Selina Kyle is afraid of him, Alfred, after hearing rumors about him and seeing footage of him at the Stock Exchange, is convinced that Bruce doesn't stand a chance against him. And as the film progresses, he traps nearly the entire police force in the tunnels beneath Gotham, then takes over the city, but before he did that, he seemingly killed the Batman. For months he is the terror of the city, and the few remaining police officers don't try to face him, they just try to stay out of his way.
Batman becomes this himself even to Bane judging by Bane's reaction to seeing the Bat-Signal on the bridge.
Verbal Kint Keaton once said, "I don't believe in God, but I'm afraid of him." Well I believe in God, and the only thing that scares me is Keyzer Soze.
Brick Top in Snatch. Merely poking his head through a door is enough to make hardened killers soil themselves. When asked, "Do you know who I am?" the bad-boy yardie Lincoln simply lowers his head and meekly replies that yes, he does.
Terminator: The T800 in the first film. In the sequel, Sarah Connor reacts with horror when she sees the new T800 for the first time. By the time the T1000 comes along, she's better prepared for it.
Indeed, the first time she sees the T800 in T2 is the only time in the entire movie when she absolutely panics.
Nearly every character treats the transformation from Bruce Banner to The Incredible Hulk as a threat comparable to that of a nuclear bomb.
The Stinger of the movie shows that humans have reached this status among the Chitauri (who, according to Thor, have this reputation themselves) by beating the crap out of their invasion force in short order before nuking their mothership.
Thor (to an extent) and the rest of the Asgardians are also this to SHIELD, causing them to use the Tesseract and the remains of the Destroyer to create super-weapons in order to fight them, along with other extra-terrestrial beings Loki's actions also make Fury desperate enough to assemble the Avengers in the first place.
In Apocalypse Now, Colonial Kurtz is this. It is at one point mentioned that the Viet Cong in the area appear to be fleeing in terror due to the brutality of his tactics alone.
The velociraptors in the Jurassic Park series are this. Remember that dark little tune that plays at the opening of the first film? It becomes their Leit Motif, to the point that you'll hear it at the mere mention of Velociraptors, shortly followed by a barrage of Oh Crap and Why Did It Have to Be Snakes? reactions from everyone...including people who don't even know what a Velociraptor is.
The Hessians in The Crossing owing to their rigid battle formations and their slaughter of surrendering troops at Brooklyn. Captain Heineman of the Pennsylvania German troops even asks if he can discuss the attack with his men beforehand rather than on the day so they won't be too terrified to attack troops they think of as "devils."
In Hellraiser: Inferno, the Engineer is a near-legendary figure in the criminal world and tales of his insane depravities abound. Every time Joseph asks around for information on him, his informants recoil in terror.
Captain America: The Winter Soldier has the titular villain. Black Widow is even more apprehensive of him than she is of Loki and the Hulk, and it becomes clear early on that the only person capable of stopping him is Steve.
The Film/Newsies ain't afraid of Brooklyn. ...But Spot Conlon, he makes 'em a little nervous...
Played for laughs in The Freshman, with Matthew Broderick and Marlon Brando. When an attractive young woman (played by Penelope Ann Miller) interrupts Clark Kellogg's (Broderick) film studies class looking for Clark, the teacher is less than impressed. When she announces herself as the daughter of Carmine Sabatini (Brando, channeling Vito Corleone), the teacher just about shits a brick; "Jimmy the Toucan?!?"
Invoked by Lord Blackwood in Sherlock Holmes, who deliberately cultivates an image of himself as a devil-worshipping Evil Sorcerer and Antichrist figure because his plans hinge on using fear to control others. Judging by the terrified crowd of Doomsayers that gather outside Parliament on the day when his plan reaches its climax, he did pretty well in that regard.