Normally, people who are calm tend to speak in a clear, even voice that doesn't vary too much from word to word and is immensely reassuring to the listener. This isn't always a good thing, however. A perfectly monotone voice usually means just the opposite of sanity, safety, and cause for reassurance; usually, it means the speaker is mind-controlled, crazy, an impostor, or is being threatened with death. In these cases, the Creepy Monotone is a sort of Glamour Failure to clue in the hero that any of a dozen things may have just gone wrong.
Usually, the creepy monotone varies from a calm monotone in that no word or syllable is stressed at all, even when they should be. This is the difference between saying "Oh hello!" and "Oh, hello." Even Spock Speak sounds more natural and less unsettling by comparison. Contractions are often omitted, as are specific or explicit mentions of names and facts, depending on the cause of the monotone. Here are some common scenarios for the Creepy Monotone.
"Yes, I am fine. I'll be even better once I load my gun, though." The character has just suffered a Heroic BSOD or one too many rounds of Break the Cutie and/or is about to go completely homicidallyberserk. Usually paired with jittery motions, twitching, or a Broken Smile.
"Good morning annoying sibling, I am your sister Melanie." An evil duplicate (Robot, Clone, Shape Shifter, Doppleganger, or what have you, even zombie/ghost possession/mind control) has replaced the character. Their tell will usually be not knowing names and facts about their host and friends, knowing too much about their host, assuring everyone that they are Most Definitely Not a Villain, or a radically different personality. May be Too Dumb to Live at things the real one, or even anyone without too much Fish Out of Temporal Water and minimal Genre Blindness, could do perfectly fine. A protagonist doing this, impersonating the hero while the hero is doing something else, is almost inevitably going to be the one that will be the most idiotic and provide either Fanservice or tons of Squick and Fan Disservice.
"I am sorry. If it's any consolation, this likely won't hurt much." If a character is introduced with a creepy monotone, then all bets are off. If you're lucky, they're just an Emotionless Girl or The Stoic, but odds are they're the Ultimate Evil, an Evil A.I., Ax Crazy, or some other seriously dangerous character.
Sawyer from Black Lagoon is a Type 5 example. She's Ax Crazy, but speaks with a Creepy Monotone due to the fact that her voice box was damaged and she needs an artificial voice box to speak.
In the last OVA, after being possessed by an evil doll spirit, Akane from Ranma ½ starts talking in a low monotone voice, even while Showing Off the New Body.
Digimon Frontier's Dark Trailmon. He's actually very HAL-inspired, in design and in voice. (Ironically, he's not evil, just creepy: you expect the Dark Trailmon that you meet in the Dark Terminal during a hallucination caused by Duskmon, the Warrior of Darkness, after he ambushed you and kicked your butt on the Dark Continent to be a little...dark.)
Prior to that, Adventure had Machinedramon, who was dark.
Many Nightmares from Digimon Tamers came from J-Reaper, who was even darker.
Now THAT'S an Understatement!
Legato Bluesummers of Trigun almost always spoke with a creepy monotone (or simply very calm) voice.
Subverted in the manga: after being crippled by Knives for trying to kill Vash, he turns Axe Crazy, but still talks with the creepy monotone.
Johan Liebert from Monster constantly speaks in a calm, quiet monotone as part of his Dissonant Serenity.
Paul von Oberstein from Legend of Galactic Heroes has a trademark Creepy Monotone and is one of the grey characters of the series. While he has thrown his lot in with Reinhard, he also has his own goals and apparently has little need for the fellowship of the other admirals. His actions lead to the death of Siegfried Kircheis, Reinhard's closest friend in an assassination targeting Reinhard. He is also a participant to the events that lead to Oscar von Reuental's rebellion, although he later exhibits something not unlike sympathy.
In Higurashi No Naku Koro Ni, speaking in Creepy Monotone tends to show up in the main cast whenever things about the Town with a Dark Secret or Oyashiro-sama's curse start getting unearthed. More specifically, those under the influence of Hinamizawa Syndrome start imagining the people around them doing this, compounding their paranoia.
The Anti-Spiral leader in Tengen Toppa Gurren Lagann, and Nia when she's changed into an Anti-Spiral. Once the protagonists get the better of him, he snaps and starts getting Hot Blooded.
Shino Aburame from Naruto. (When he talks, anyway.) Somehow, this makes him even creepier than being a living hive for 4 million insects would by itself.
Gaara would fit this. Even after his Heel Face Turn, he still retains his emotionless, monotone way of speaking. Old habits die hard...
And Itachi Uchiha. Until he and Sasuke have their final battle. Then he goes ape-shit crazy and screams. A LOT.
When Lilika in Burn Up! Scramble uses her Psychic Powers, she gets Mind-Control Eyes and speaks like this. Usually, she blurts out something embarrassing about Rio.
R. Dorothy Wayneright from The Big O is monotone because she's an android (well, gynoid, technically). However, she is notemotionless, making it hilarious when she verbally abuses Roger in a calm, soothing voice.
"You're a louse, Roger Smith."
Rei Ayanami from Neon Genesis Evangelion. She's practically the poster child for this trope, when she does talk.
Though she still has noticeable subtle changes in tone if you pay attention. So it's not completely monotonic, actually. The Creepiness is up to the viewer to behold.
By that extent, Yuki Nagato from the Haruhi Suzumiya megamoechise is also rather limited in expressing herself through speech.
Crona does this more notably, using this as a normal tone of voice. His/her voice becomes sing-song and insanewhen his mind is snapped by Medusa, complete with a Slasher Smile and Laughing Madness.
Vincent Volaju of Cowboy Bebop. He never raises his voice.
Given that she's an Emotionless Girl that drags people down to hell, Ai of Hell Girl always speaks like this. The times when she doesn't is normally a time that you're REALLY screwed.
In Death Note, L and Near are both prime examples of this trope.
Rorschach from Watchmen speaks in a low, growly monotone (other characters remark on its unsettling quality) with odd, near-Hulkspeakclipped sentences. "Yes. Good night. Remember it often." He has flashes of eloquence, too, which are unnervingly at odds with this style of delivery.
His mode of speaking is shown by his unique speech bubbles, with no words ever bolded or italicised for emphasis like the other characters'. By contrast, his speech bubbles in flashbacks to before the Blaire Roche case indicate a totally normal voice.
His speech in general is a lot more relaxed and human in the past, and he seems more open to other's opinions (Saying something like "Well, I disagree..." instead of "Wrong.")
In Men In Black, the bug in the Edgar suit demands sugar water from Edgar's wife, in a type-2 situation. OK, so his Creepy Monotone is very gruff and hostile-sounding, but that basically matches Edgar's pre-bug personality as well.
Hugo Weaving in The Matrix films. "As you can see, we've had our eyes on you for some time now, Mr. Anderson." He also stresses his words oddly and unnaturally, almost like a synthesiser. His exchange with Laurence Fishburne about how humans were not really mammals, but a disease, was genuinely creepy.
Any and all characters in Sin City, including the heroes, have an extremely dry and calm manner of speaking, bordering on Creepy Monotone. This is exemplified with Marv, who always speaks in a soft, calm manner, bordering on the nonchalant, even when brutally torturing and murdering somebody. Roark Jr, before his run-in with Hartigan, speaks almost like HAL. After that, though, he's a lot more expressive.
HAL 9000 of 2001: A Space Odyssey speaks in an eerily calm and soothing voice, though he occasionally displays some emotions: prideful and even apologetic and, at the last, fearful, making him the most developed character in the film.
Uncle Charlie from Shadow of a Doubt
Bruno Anthony from Strangers on a Train
Hannibal Lecter from the The Silence of the Lambs, Red Dragon, Manhunt, Hannibal, and Hannibal Rising. Anthony Hopkins based his performance on HAL 9000
Travis Bickle from "Taxi Driver" often does this, especially when narrating.
A type 4 Creepy Monotone is apparent in Jonathan Crane in Batman Begins, after he's been given a massive dose of his own fear toxin and Batman, who's already kind of a scary guy, is interrogating him.
"...Dr. Crane isn't here right now...but if you'd like to make an appointment..."
After Selina Kyle is almost killed by her boss Max Shreck in Batman Returns for knowing too much, she repeats the same words that she said upon entering her apartment in a previous scene, only in a Creepy Monotone of the fourth variety: "Honey, I'm home. Oh, I forgot, I'm not married." This turns out to be a prelude to Selina's impending Freak Out and transformation into Catwoman later in the scene.
Bart, a rogue cop in Southland Tales, provides an example of type #5. He flatly insists on tagging along to a (fake) domestic disturbance with Taverner and Santaros and executes the couple on arrival. A creepy monotone delivered by Jon Lovitz is surprisingly unnerving.
It Came from Outer Space (1953). The aliens who've copied human forms talk this way, severely flipping out the real humans who don't believe their repeated claims that they don't mean any harm.
Not just monotone; these voices are like someone speaking inside a box; unnerving in the street or at home.
28 Days Later has a variation, where a drugged Hannah is monotonously scaring the soldiers by telling them how Jim is killing them all.
Full Metal Jacket: "Seven. Six. Two. Millimeter.... Full... metal... jacket..."
Dr. Manhattan in Watchmen. In one scene, Ozymandias remarks that he knew that Manhattan still had feelings; they were just too subtle for others to notice. He uses this to his advantage.
John Malkovich in the 2000 TV miniseries of Les Misérables, perhaps as a result of trying to avoid any accent as he is not talking in his mother language.
The citizens of Sandford in Hot Fuzz do this after Nick Angel exposes their dark secret.
The evil townspeople of "Nilbog" also do this in Troll 2 while trying to force the protagonist to eat a poisoned bowl of ice cream and, in the process, prove that even a creepy synchronized monotone can turn into hilarious narm (or maybe even disturbing Fetish Fuel) with the right line:
"Open your mouth, my little friend! Please, open it!"
The robot GERTY in Moon is voiced by a very monotone-sounding Kevin Spacey. In the end, the trope is subverted as GERTY turns out to be mostly benevolent, going so far as to perform a Heroic Sacrifice.
Count Rugen in The Princess Bride is a particularly scary example, because the entire rest of the film falls soundly in the World of Ham category. He stands out by being completely calm and utterly serious.
"As you know, the concept of the suction pump is centuries old. Well, really, that's all this is. Except that instead of sucking water, I'm sucking life. I've just sucked one year of your life away. I might one day go as high as five, but I really don't know what that would do to you. So, let's just start with what we have. What did this do to you? Tell me. And remember, this is for posterity, so be honest — how do you feel?"
Sy Parrish in "One Hour Photo" spends the majority of the film talking in a very soft-spoken, almost robotic monotone, reflecting his disturbing lack of a personality, although he does show emotion at times, especially near the end of the film when he starts to lose it.
The aliens in the first Invasion of the Body Snatchers, when no real humans were around to fool. Such as "I put the pod in the baby's crib. Soon there will be no more crying."
The nameless narrator in Fight Club sometimes slips into this, both in his narration and his dialogue in the film.
Literature
Mr. Jonathan Teatime from Discworld unnerves people with his creepy monotone.
Lord Voldemort speaks in a calm, flat tone of voice; this, perhaps even more than his use of Soul Jars and his utter lack of compassion, makes him terrifying. Except for when he gets agitated. It comes across more as him trying to achieve this trope but failing every now and again.
The demon from the Neil Gaiman short story "Other People" speaks in "a voice that carried with it no sorrow, no relish, only a dreadful flat resignation." It is utterly expressionless for all of the story.
Myrddraal from The Wheel of Time have voices that are described as sounding like crumbling bone and are utterly devoid of emotion or inflection. Not only is this incredibly creepy, but it makes Shaidar Haran, the only Myrddraal who does show emotion (because he's possessed by a "shadow", as Word Of God describes it, of the Dark One), even more disturbing by comparison.
Brinkley was at the door, begging me to come out and let him ascertain the colour of my insides; and by Jove, what seemed to me to add the final touch to the whole unpleasantness was that he spoke in the same respectful voice he always used. Kept calling me 'Sir,' too, which struck me as dashed silly. I mean, if you're asking a fellow to come out of a room so that you can dismember him with a carving knife, it's absurd to tack a 'Sir' on to every sentence. The two things don't go together.
What makes it even creepier is that the monotonous "Bored now" is the exact line used by an alternate version of Willow wherein she was an evil badass vampire chick. Dark Willow was basically her vampire double sans the vampire.
Subverted in Dexter: Half the fun of most dialogues the title character takes part in resides in the way Michael C. Hall delivers his lines, in an emotionless creepy monotone that should trigger the "serial killer alarm" in the minds of even the most oblivious of the other characters. Except, of course, it never does.
Inverted when he snaps and kills the used car salesman for insulting Rita. Cue scared "he's freaking crazy!" reaction.
Eugene Victor Tooms, from The X-Files, bare-ly has an-y in-flec-tion at all and talks real-ly slow like he's re-tard-ed. It's ser-i-ous-ly freak-y.
So does Donnie Phaster, arguably the show's creepiest villain. Go watch "Irresistible" at 2 AM if you don't believe me.
In the Firefly episode "Objects in Space", River announces to the bounty hunter Jubal Early that she has "melted away" into the ship Serenity, becoming part of it, in a Creepy Monotone. It becomes even more chilling when she alters her tone just a tiny bit for the line
"Not talking to River. You're talking to Serenity. And Early? Serenity is very unhappy."
Summer Glau is good at creepy in general. In The Sarah Connor Chronicles, Cameron regularly speaks in a constant, soft-yet-creepy monotone. However, the show also plays its absence to excellent effect. The absence of the Creepy Monotone we're used to is what made the scene where Cameron recites not only word for word, but inflection for inflection a "classmate's" emotional bathroom rant for the principal creepy.
Similarly, in the second season premiere, the steady shift from Cameron's Creepy Monotone to her desperate, terrified pleas to John to a screaming declaration that she loves him while he's trying to take out her chip makes for a chillingly awesome scene.
In fact, whenever she's not speaking in her monotone voice tends to be even more unsettling, because it's so obvious to the audience that she's completely faking it.
And in the episode "Allison From Palmdale", the use of the Creepy Monotone and its absence makes an already chilling episode that much creepier.
Also, the Cybermen in the 60's and current. Especially the 60's, when they had creepy, emotionless machine-like voices.
The Daleks use a mechanical, staccato voice delivery, but they tend to increase both speed and volume for emphasis. Also, there's quite a bit of variation of individual voices. Creepy, yes; a monotone some of the time, but intensely emotional.
The Daleks' speech mannerisms are actually very monotone. The only difference from other examples is that the single tone used isn't flat apathy, but rather a consistent bent of shrieking hysterical rage. When they're NOT grating out staccato bursts of antipathy, it usually means something's very, very wrong.
Used to great effect in "Silence in the Library", where an AI retelling cries of panic and pain in utterly emotionless Creepy Monotone made the situation seem scarier than it would be if they were reproduced verbatim.
The creepiness in The Impossible Planet consists mostly of the Creepy Monotone of the Ood and the computer system being possessed by Satan.
Sylar from Heroes could possibly pass for a perfectly ordinary, non Serial Killer type, except that he seems capable only of a Creepy Monotoneor screaming and uncontrollable murderous rage. No middle ground.
Sylar: This is usually the part where people start screaming.
The Observer in Fringe. On first seeing him, this trope leads the viewer to believe that he's got something devious going on, but he turns out to be more ambiguous than that.
The Borg from Star Trek speak like this, along with Voice of the Legion. Individual Borg that have been separated from the Hive Mind also start off with a creepy monotone, though as they develop their own personalities, they usually segue into Deadpan Snarker or Spock Speak.
Award for creepiest borg monotone goes to Locutus' line: "Your resistance is hopeless...Number One."
It's worth noting that Picard used the Locutus monotone while interrogating the liberated drone Hugh, who recognized Picard as Locutus.
LOST. Benjamin Linus. "Of course, if I was one of them, these people that you just assume are your enemies, what would I do? There would be no balloon so I would draw them out to a really secluded place, like a cave or some underbrush, a good place for a trap... an ambush. And when your friends got there a bunch of my people would be waiting for them. Then they would use them to trade for me. I guess it's a good thing I'm not one of them, huh? ...You guys got any milk?"
Robert Stack would often host his segments on Unsolved Mysteries in what was supposed to probably be a very flat, newscaster-type voice. Unfortunately, the tone of his voice and the creepy nature of the show sent it careening into this pretty quickly.
Thom Yorke, the singer, sometimes actually slips into this, especially on the albums Kid A and Amnesiac.
"Hide and Seek" by Imogen Heap.
Nu-Italo (eg. Eiffel 65) songs often used vocoders to this effect.
"Domo arigato, Mr. Roboto".
"I Tried So Hard to be Good" by The pAper chAse.
OK Go's cover of The Muppet Show theme song. Especially creepy when you realize it's for a kids' movie.
Tabletop Games
On the few occasions in Warhammer 40000 that Necron Lords have spoken, they have been unusually polite and cultured speakers possessed of a truly chilling calm, which may make some sense, given that they are the still-sentient leaders of a race that now exists as, for all intents and purposes, undead robots.
"Lucky creatures... At long last... you have found... the tranquillity... of death..."
This is one of the suggested options for the voice of Friend Computer in Paranoia.
Videogames
In Phoenix Wright Ace Attorney - Trials and Tribulations, Viola Cadaverini is said to speak with a creepy monotone, laced with subtle death threats.
The G-Man from Half-Life 1 and especially 2 is a variant of this, he speaks in semi-monotone but stresses the wrong words and pauses (and fails to pause) in all the wrong places. ex. "Not that I wish to-imply that you have been... sleep-ing on the-job"
A version of this appears in Half-Life. Black Mesa's PA system is created via a sort of voice synthesizer that assembles pre-existing voice files into phrases. This is initially used as a generic announcer, but it is later taken under control of the enemy soldiers and used to threaten the protagonist himself.
The Combine announcer combines this with medical terminology: She/it sounds like she's/it's describing a medical procedure, not an urban counterinsurgency crackdown.
Max Payne, in both games. It's particularly striking in the first game, since the actor playing him, Sam Lake, looks quite humorous and has a flamboyant outfit (leopard prints).
This is how the protagonists know that something is wrong in the titular star system in the game Nova 9. They get a brief Distress Call that is cut off, then, shortly after, receive a message delivered in creepy monotone saying that everything is fine and to disregard the previous message.
The animated Statues in Thief: Deadly Shadows. They have one purpose only and, as a result, come across as rather single-minded. "A noise and find and crush and kill and crush and kill..."
Now, Sheogorath from Oblivion is known as the Lord of Madness, so unbalanced tendencies are to be expected. Normally, in fact, he's rather charming and downright giggle-worthy with his fake-Scottish accent and habit of cheerily threatening life and limb (and mental integrity). However, when he suddenly becomes very quiet, his eyes narrow, and he speaks very, very softly, you're reminded that you really ought to be terrified of this guy.
Portal proudly sports GLaDOS, who has a sort of musically random inflection, but in a very mechanical way. This is emphasized when she uses a word or phrase more than once in a short period of time. Also, "Wheeee..."
The turrets also have the same type of voice (and the same voice actress), but with a more cute than creepy inflection (which doesn't say much).
You spend so much of the game listening to that voice, right from the very start, that when you destroy GLaDOS' Morality Core and she switches from robotic monotone to an emotive, fluent female voice, it's actually far creepier than the monotone, because GLaDOS talking like a normal person is simply not right.
The subtitles even describe it as outright seductive. No, this is NOT a good thing.
In BlazBlue, the "final boss" in Arcade Mode is ν-13 (pronounced "nu-thirteen", 'cause that's a Greek letter dontchaknow), who is introduced with a Creepy Monotone and, yes, is an Emotionless Girl with an Evil AI who becomes Ax Crazy around certain people, to the point of being quite Yandere. In other words, bullet number 5 at the top of this page. Like GLaDOS, ν-13 shares a voice actor with another character.
Lambda-11 of the sequel shares the same voice actress as Nu and speaks in a creepy monotone as well, albeit in a slightly different tone. This troper has only played the Japanese version and so is not sure whether it's the same in English, but Lambda's voice is much more monotone than Nu's (either due to her voice actress getting better or because of Lambda's story, or both)
The Many speak this way in System Shock 2. They have multiple voices (an electronically-pitched rumble, a whispering masculine voice, and a nearly singsong feminine voice) and one or two of them sometimes have inflection, but the majority of it is in a serene monotone. "How can you choose cold steel over the splendor of flesh?" The contrast between the Many's monotone and SHODAN's stuttering and wildly varying inflection and pitch makes for one of the creepiest aural dichotomies the gaming world has to offer.
Also, the Many-controlled AI, Xerxes (who resembles HAL9000 much more than SHODAN): "Decompression in five seconds. We regret any inconvenience." He is also quite dissonantly serene; he announces workplace accidents, the number of shopping days until Christmas, meal times, and security breaches in the same tone as the freaky messages programmed into him by the Many.
In the Kingdom Hearts series, nearly every single Organization XIII member talks like this at least once, with Saix being the most notable example.
But the best example comes from 358/2 Days, towards the end of the game, right before the fight against Xion. Excuse me a moment, I have to go repress the memories.. again.
"You're next, Roxas. I have to make you a part of me too."
The promo material for Mass Effect 2 features a geth named Legion speaking in this manner. It is absolutely terrifying when you hear him speaking on how the geth use fear in such a cold mechanical voice.
Legion: We do not experience fear, though we understand its effect on you.
Then you play the game and find out the promos lied to you, and Legion's voice just makes it adorable.
The Elcor sound like this to most sapients since they communicate inflection through pheromones and minute gestures, so they explain what they're saying.
The Reapers speak this way as well, particularly Sovereign. Harbinger carries slightly more inflection, but is still consistent in tone whether he is ASSUMING DIRECT CONTROL or remarking on how irritating the protagonist is.
"Shepard. You have become... an annoyance."
The Tranquil in Dragon Age: Origins - Mages who have undergone a sort of magical lobotomy and are now incapable of emotion. The Sloth Demon also has one.
One word: Hespith.
First Enchanter Irving has a bit of this, though it makes him sound more like a tired old man rather than crazy.
Algalon of World of Warcraft, up until he loses his cool and admits his convictions may have been in error. He'll unleash hell on you before that happens, though.
S.T.A.L.K.E.R: Call of Pripyat: You don't want to hang around The Monolith Fighters, but there are moments where their Creepy Monotone can be quite memorable.
The "Milkman Conspiracy" level from Psychonauts is the mind of a paranoiac, where Government agents with the flimsiest of disguises spout hilarious monotone oneliners to maintain their cover.
Housewife: As I grow older, my husband will desire me less sexually, but will still enjoy my pies.
Grieving widow: Why. God. Why.
Gardener: Plants need water poured on them, because they have no hands to hold glasses of water.
Assassin: They got Freddy. Poor Freddy. He was such a good secret agent. I mean assassin.
Phone Repairer: I can listen to any phone conversation that I want, but do not because of my sense of professional responsibility.
Helicopter Pilot: "elicopters can go up and down. Helicopters move sideways too, but not as fast as planes.
The entire village of genomes from Final Fantasy IX are said to be emotionless.
The Martians of Jeff Wayne's War Of The Worlds speak like this. A notable exception is their trademark "ULLAAA!" from the musical, which can sound triumphant or sad depending on the situation.
Web Comics
Homestuck's Gamzeepossibly speaks in monotone; it's hard to be certain exactly how his text quirk would be vocalised. At any rate, he later goes off the deep end, and upscales his wHiMsIcAl CaSe AlTeRnAtIoN to whole lines of text, meaning that he alternates between barely audible and SCREAMING IN RAGE.
El Anticristo and Andale Ramiro, two Hispanic dudes from Youtube who say the most aggressive things about anything via a by-definition-monotonous speech synthesizer, are famous for doing that.
The hovercat from Water Human. Like Gary above, he's voiced by Microsoft Sam.
There are various internet CGI cartoons featuring anthropomorphic pig-things speaking with monotone voices.
Western Animation
Terminal, a one-shot Batman Beyond villain, is another good one. This from the man (Michael Rosenbaum) who went on to play the Flash.
This is especially creepy considering how Terminal is the leader of a gang of Jokerz. "You're not laughing. He's not laughing."
Mr. Freeze on Batman The Animated Series never really deviated from his cold, chilling (no pun intended) monotone, providing juxtaposition to the emotional depth of the character. Needless to say, it was effective. Word Of God has it that his voice actor, Michael Ansara, struggled with this element of the role — his instinct was to act, and he had to be constantly reminded to be flat and robotic.
Possibly especially so in Batman Beyond, where he stops being simply apathetic and starts being straight up merciless.
In one of The Simpsons' Halloween specials, Bart is turned into a vampire. He rejoins the family and monotones, "Hello mother. Hello father. I hope you were well during my brief and uneventful absence."
Then there was the one where Lisa has to tell Homer that Bart had rented a car with a fake ID and was trapped in Tennessee. Homer's face goes red and he says calmly, "Yes. That's a real pickle. Would you excuse me?" He puts on a radiation helmet and screams incoherently for a while, causing the faceplate of the helmet to fog up. He then takes it off and says, now using the monotone again, "Alright, I have thought this through. I will send Bart the money to fly home. Then, I will murder him."
Slade is played by Ron Perlman, who used the exact same monotone when narrating as Firelord Sozin from Avatar The Last Airbender in "The Avatar and the Firelord."
The Twins from Superjail! speak in a low, quiet, gentle monotone voice - a stark contrast to the Warden's loud, flamboyant, inflected way of speaking.
While everyone might want to forgetMega Man's "Curse of the Lion Men", it does fit here. After Tar flash-reprograms Wily's robots and Roll, Protoman very flatly tells him that he's now their leader. Made even more unsettling since no one else being mind-controlled during that episode invoked this trope (except perhaps Roll).
Played for laughs in Futurama with the Hypnotoad. Anyone it hypnotizes immediately speaks in a creepy monotone and espouses the glory of the Hypnotoad.
Also parodied in the Futurama episode "Raging Bender", when Hermes comes back from vacation with a green slug on his head and explains in a Creepy Monotone that they had to make an emergency stop on the Brain Slug Planet. Throughout the episode, he tries to trick the others into wearing brain slugs.
Shockwave of Transformers Animated. He even gives a Shout Out to 2001: A Space Odyssey HAL, saying "I'm afraid I can't let you do that" to Ratchet. In his disguise as Longarm, he talks normally. Shocky also has a single red eye.
Tino from The Weekenders started talking like this when he was made fun of for crying during a showing of Romeo and Juliet, so he decided to become emotionless.
The episode "Operation: D.A.T.E" has the Delightful Children using a mind control device on a lot of kids they invited to a party in their mansion. As a result, they get Mind-Control Eyes and keep saying "Join us..." in a monotone sounding voice.
Her flat-tone delivery is most likely one of the reasons why Daria is so unpopular in school. The audience usually finds it endearing, but to most other people, she's "the freaky quiet girl".
Real Life
A bit of Truth in Television: behold flat affect, a common symptom of Post Traumatic Stress Disorder and the psychotic disorders (which includes schizophrenia).
Stephen Hawking speaks like this, though it's because of the synthesizer he has to use to speak at all. He's actually quite personable. His lectures certainly draw crowds.
It's not just Hawking. Anyone who speaks using an artificial voicebox has no choice but to use a monotone, as the mechanism doesn't allow for inflection and tone. Later, Hawking was offered improved software that could affect tone better and use a more appropriate accent; he turned it down because the synthesiser is recognised as being his voice.
David Tanny uses a voice for his songs and podcasts that is basically a cheerful monotone. Especially unsettling when what he sings about contains Squick, as it frequently does.
Used by Robin Williams to show one of the ways you can find out if your neighbors have been taken over by aliens.
In an interview, Alfred Hitchcock explained that raving lunatics are not scary. He said it was the dead calm voice you can't reason with. He made a finger gun gesture and said (in a dead calm voice) "I don't want to do this, because my mother always said you shouldn't hurt people." Very creepy.
