Walk like an angel
Talk like an angel
But I got wise
You're the devil in disguise."
The Devil is an evil, sneaky fellow who sometimes likes to go incognito among the living to manipulate people and stir up some sin, or maybe just tempt some mortals and secure a few more souls for himself. Alternatively, maybe he has simply sent an agent of some sort to do his dirty work for him. Either way, there's a demon hiding among the living and this time, he may well have a less obvious name than Louis Cypher.
- Xellos from Slayers. Among his Always Chaotic Evil kind, he's the most powerful one (not counting godlike Dark Lords), but prefers to use manipulation rather than violence. Two of the most powerful Dark Lords actually died from the consequences of one of them employing Xellos against the other the second-strongest managed to injure him in one-on-one battle, but he still got away. He's also honorable in his own way and can be a good company when he wants. In his world, few humans have thorough knowledge of demonology, so he walks among them under his own name and title. Not to mention that his self-proclaimed title is "Mysterious Priest". If people assume "Priest" always means "user of White Magic", it's their fault.
- Ronnie Sukiart from Baccano! is the demon who gave the alchemists immortality taken human form.
- Sistine Chapel: In order to get The Temptations of Christ right, Satan needs a disguise to cover his wild, hideous body. Naturally, he goes for the most innocent thing he can find: a black robe that covers his whole body. Well, the bat wings, but Christ is too polite to make a point of it.
- In the Superman comics in the early 90s, it was revealed that publisher Colin Thornton, who had hired Clark Kent away from The Daily Planet to serve as an editor for Newstime, was a mortal disguise used by the demon Lord Satanus.
- Welcome to Tranquility has Funky Freddy Beasel, a seemingly ageless radio DJ who turns out to be a satanic demon known as The Host.
- A common situation in Jack Chick's "Chick Tracts"' (for example, Somebody Goofed). A person is considering accepting Jesus, but a friend convinces him not to "you'll lose all your friends" or "you have plenty of time for that later". The person dies unsaved, goes to hell, and sees who his "friend" was all along.
- This trope was invoked in The Last Temptation of Christ, during Jesus's final temptation while on the cross. A young girl introduces herself as an angel, says that Jesus has done enough, and offers him an escape from the cross. This girl accompanies him as a friend through a happy life with a wife and children. But this friend is actually Lucifer, and these years after escaping the cross were All Just a Dream to tempt Jesus into abandoning his role as Sacrificial Lion. As soon as Jesus rebukes this temptation, the illusion ceases and he instantly returns dying on the cross, accepting it as his destiny.
- John Milton in The Devil's Advocate. He's able to pass for human without fail, only dropping hints because he wants the protagonist (who is really his son) to find out that his boss is the Devil himself.
- In Susan Cooper's The Dark Is Rising series, Blodwen Rowlands turns out to be The White Rider, one of the most powerful Lords of the Dark (the other being The Black Rider).
- Crowley from Good Omens. He is Hell's field-agent on Earth, who has taken the guise of a bon viveur by the name of Anthony J. Crowley.
- The wizard Pralaya in The Wizard's Dilemma (Diane Duane's Young Wizards series) is "overshadowed" by the Lone Power (meaning, possessed by the Devil, basically).
- Played in a wonderful subversion in Heinlein's Job: A Comedy of Justice when the protagonist finds out that the only friend he and his wife made through their ordeal was actually the devil himself. Not only had he shown him genuine mercy and friendship, he had turned down the bet with God, thinking it sick and cruel.
- In the backstory of The Lord of the Rings, Sauron presented himself to the Elves of Eregion as 'Annatar', the Lord of Gifts, and with their help made the Rings.
- In My Vampire Older Sister and Zombie Little Sister, it's revealed that Lilith, the queen of succubi, is none other than the main character Satori's stepmother. Though she's not, strictly speaking, a villain.
- In Raise Some Hell, this trope is played straight, in the case of Dean Montgomery.
- The Master and Margarita: Woland is actually Satan disguised as a professor and magician while visiting Moscow.
- In an old fairy tale from Piemonte (North-West of Italy) there's a tale similar to the one of Blue Beard, where the Big Bad is the devil disguised as a human who takes human girls to his castle (which hides the entrance to Hell in a secret room) to work for him. Furthermore, his nose is made of silver.
- In one episode of Quantum Leap, Sam discovers that the "Al" who has been advising him is a fake, and is actually the Devil. Or Was It a Dream??
- Ultraman Nexus: Dark Zagi disguises himself as one of the human characters until his body is fully restored in the last episode.
- In The Twilight Zone, the Devil and his underlings usually appear in the guise of ordinary people.
- In "The Howling Man", he appears to be some poor guy who's been imprisoned by an apparently crazy monk, but when someone takes pity and releases him his horns and tail reappear.
- In "Escape Claus", the Devil appears as a man named Cadwallader, although he all but admits that it's a false name "It has a nice feeling on the tongue.", and while he never admits to being the Devil, he makes very little attempt to hide the fact apart from his human form.
- Mister Pip from "A Nice Place to Visit" is Satan, or at least one of his demons, disguised as a guardian angel... who looks human.
- Professor Daemon from "The Chaser" is implied to be this trope.
- Mister Smith in "Printer's Devil".
- Miss Devlin in "Of Late I Think of Cliffordville", although she drops the act once the protagonist figures out what she is.
- In Ashes to Ashes (2008), DCI Jim Keats who appeared to be a helping hand to Alex is revealed to be the Devil in the Grand Finale. Gene Hunt possibly knew this right from the first episode of Season 3.
- Dr. Hannibal Lecter or at least, that's the subtext of the series. During his audition for the role of Lecter, Mads Mikkelsen pitched his take on the character as a literal manifestation of Lucifer, and showrunner Bryan Fuller ran with it.
He talked about the character not so much as 'Hannibal Lecter the cannibal psychiatrist', but as Satan this fallen angel who's enamored with mankind and had an affinity for who we are as people, but was definitely not among us he was other. I thought that was a really cool, interesting approach, because I love science fiction and horror and not that we'd ever do anything deliberately to suggest this - but having it sub-textually play as him being Lucifer felt like a really interesting kink to the series. It was slightly different than anything that's been done before and it also gives it a slightly more epic quality if you watch the show through the prism of, 'This is Satan at work, tempting someone with the apple of their psyche'.
- Satan from Old Harry's Game disguises himself whenever he visits Earth (except when he's going to scare somebody).
- Applegate from Damn Yankees. Referencing, of course, that particular apple, the first temptation of man; Lola is one of his newer ones.
Joe: Who are you?
Applegate: I am quite a famous character, Mr. Boyd. I have historical significance, too. In fact, I'm responsible for most of the history you can name.
- Later, a passing stranger asks him, "Are you anybody?" He replies, "Not a soul."
- Basil Bob in The Tempest Chronicles
- In Demon: The Descent, every demon is in disguise: a demon without a Cover has a lifespan comparable to that of a vampire going for a jog in the park at noon on a sunny day. Many painstakingly build effective disguises by squirrelling away bits of other people's lives or even stepping fully formed into the life of someone who's made a soul pact. Many of the more powerful abilities of the Unchained fray their Cover a bit, and "going loud" sacrificing their Cover for a massive, if temporary, power boost is viewed as a Dangerous Forbidden Technique and considered "the nuclear option", because few demons who pull it live long enough to do so twice.
- Julie from Confess My Love turns out to be a demon who is waiting to take Willie's soul to hell.
- In Hellgate: London, the story's narrator / hero's sidekick Murmur turns out to be the Duke of Hell with the same name. To be fair, the name's a lot more subtle than Lou Cypher, and isn't likely to mean anything to players without a background in demonology mythology and/or who aren't Shin Megami Tensei fans.
- In Phantasy Star IV, you are accompanied for the span of one dungeon by an adventurer named Seth. While his name doesn't really say anything of what he really is, using the Talk command from the menu gives subtle hints, and his abilities (most, if not all of which were used in previous fights by Dark Force) are almost a dead give away if you are paying attention. "Seth" is also the name of the ancient Egyptian god of darkness, as well as the father of all mankind in Judeo-Christian mythology.
- In Whacked!, the host and producer of the titular Blood Sport game show is Satan. He doesn't look out of place with all of the other toon characters until he reveals himself when his show gets canceled. He invented the game show to attract malevolent souls to claim.
- In The World Ends with You, The Hidden Secret Reports reveal that Sanae Hanekoma is a fallen angel that gave the taboo powers to Sho Minamimoto.
- The mysterious stranger in Red Dead Redemption never actually identifies himself (he claims, in a possibly sarcastic tone, to have forgotten his name), but he appears in locations that such a Sharp-Dressed Man has no business in being, knows a huge amount about John's past (including the name of one of the random civilians John's gang killed in their outlaw days), calls himself "an accountant, in a way", and when John gets fed up and demands answers or "[he] will not be responsible for [his] actions" he calmly tells him "Oh, but you will be responsible". John then shouts "Damn you!", the man replies "Yes, many have", doesn't seem to notice the three bullets John shoots at him, and then just vanishes. This is after a conversation where he muses over what a beautiful spot they're at, which is right where John later gets buried. It's not clear who exactly he is; common interpretations are that the man is God, St Peter, Death, or, of course, the Devil.
- In Scary Go Round, it is revealed that Ryan's friend Ralph is actually the devil rather than the figure that the comic had presented as such.
- Mr. Anon from Open Blue is a case where the name isn't quite obvious. Indeed, it doesn't even seem to mean anything, and isn't even shorthand for Anonymous. The clue for RPers, however, are his catchphrases, tendency to ask people to guess his name, and favorite activity of making deals with people.
Mr. Anon: Please allow me to introduce myself. I'm a Man of Wealth and Taste.
- The Man from Tales of MU looks like a normal human but is anything but.
- The Simpsons:
- In episode "Lady Bouvier's Lover", Marge's mother goes out dancing with Mr. Burns:
Mrs. Bouvier: I swear, Monty, you're the Devil himself.
Mr. Burns: WHA?!! WHO TOLD Y! Oh, err, heh heh...
- Not to mention the Halloween episode where it's revealed the Devil is Ned Flanders. "Always who you least suspect", indeed.
Devil Flanders: Hey, Bart.
Bart: (nonchalant) Hey.
- In episode "Lady Bouvier's Lover", Marge's mother goes out dancing with Mr. Burns: