Put simply, a character (usually a superhero) keeps his involvement in the events of the plot secret from some or all of the other characters. Usually, he does this by creating a second, separate persona for himself, which he uses while participating in the plot.
This may be done for several reasons:
Despite his superpowers, he still wants to have a normal life during those times when he is not fighting crime or evil, and he wants to keep that normal life separate from his life as a superhero. Especially if he's a vigilante and what he does is against the law.
Any combination of two or more of the above (if not all of the above).
While trying to protect that secret, the superhero is often placed in the worst kind of situations that threaten to expose it. For instance, there is the Bruce Wayne Held Hostage scenario. In more mundane moments, the superhero often has to quickly come up with a Secret Identity Change Trick in order to get out of sight. He may have to cut off most relationships to prevent this necessity. Especiallyromantic relationships.
People who guess at the connection almost invariably guess correctly. No matter how closely two superheroes resemble each other, no one will confuse them.
This is effectively a single-person variant of the Masquerade. Sometimes a select group of people are allowed to know the hero's secret identity. If they stay largely out of the action, outside an occasional errand or trap setup, they're simply Secret Keepers. If the relationship with the hero is deeper, at least on a professional basis, then the insider may be a Battle Butler. If one or both of a hero's parents were ever heroes themselves, they'll often be overjoyed rather than shocked at the child's heroism, and reveal it as part of their Secret Legacy.
See Secret Identity Identity for heroes where the secret identity isn't necessarily the "real" one. For the logical inverse, see Collective Identity.
One of the archetypal Secret Identities is that of the Rich Idiot with No Day Job. The family and friends of such a hero are usually at risk of having tea with the villain.
Experts point to The Scarlet Pimpernel, written at the turn of the 20th century by Baroness Emmuska Orczy, as one of the earliest examples of this trope. However, the Older Than PrintChivalric RomanceRoswall and Lillian has the hero work as a servant at court and fight three times at The Tourney disguised in armor, without revealing his identity; it also appears in various Fairy Tales, though in all these it is a temporary measure, and not the perpetual double identity of the modern secret identity. Bob Ingersoll considers secret identities to be actually detrimental to fighting crime. Even so, it has become a staple of the Super Hero genre, to the point where it's easier to list exceptions, subversions and variations than straight examples — such as ...
A Sub-Trope of Living a Double Life.
A Super Trope to:
In Full Moon o Sagashite, Mitsuki uses her shinigami's powers to turn herself into a famous singer. It's later revealed that Takuto was actually a member of Mitsuki's father's band when he was still alive.
In Ryuusei no Rockman/Mega Man Star Force, Subaru Hoshikawa goes out of his way to avoid revealing that he's actually Rockman
Lelouch Lamperouge, the morally gray revolutionary from Code Geass, takes on the masked Large Ham persona of Zero when he founds and leads the Order of the Black Knights against the Holy Empire of Britannia - his normal persona is that of an Ordinary High-School Student...which is also a false identity, since he's really Lelouch vi Britannia, an exiled son of the Britannian Emperor and therefore a prince.
Edogawa Conan and Haibara Ai in Detective Conan must keep secret the fact that they were youthened instead of killed by a poison used by a shadowy secret organization. The original rationale was to pretend Conan's prior identity, Kudo Shinichi, was dead, but he can't stop phoning his girlfriend using his Shinichi voice, so it seems to be a pretty open secret that Kudo is still alive. (And some people are clever enough to put two and two together and figure out who he is, too.)
Secret Identities are a major part of the plot of the anime Dokkoida?!?!. Supervillains are unleashed and given Secret Identities to test a pair of supersuits used by the heroes and promised a pardon if they can successfully unmask either one. Also, should anyone's identities become known, the whole test is null and void. Finally, due to budget constraints, everyone (heroes and villains alike) are living in the same apartment building.
Eyeshield 21 features an ace football player who hides his identity behind an eyeshield and code name. Subverted in that several cast members figure out his identity almost instantly, while others are much slower on the uptake. Further subverted in that about halfway through the series, he abandons his secret identity altogether (on live TV no less) and operates under his real name from then on, with "Eyeshield 21" remaining as a nickname.
The Eldran series both averts and plays this straight. In the first and last series, the protagonists are a class of fifth-graders, and their schools hide/are the titular robots, so its hard to keep what they do secret anyways (that and the military tried confiscating Gosaurer in its series, but the situation turned sour when it turned out it wouldn't work for them). However the second entry in the series - Ganbarugar - plays this very straight, and with justification (kinda) in that if the heroes reveal their identities, they'll be turned into dogs.
In Dragon Ball Z, there is Gohan as the Great Saiyaman. As Gohan, he's a fairly nerdy high school student. As the Great Saiyaman, he's a Large Ham crimefighter who's fond of Sentai-spoofing poses. He's also quite bad at actually maintaining the secret identity.
Most of the heroes in Tiger & Bunny have secret identities, the exception being Barnaby Brooks Jr. who is open with the public and simply does his heroics under that name. Whilst the other heroes are masked to the public, most of their family members usually know (with exceptions) and, as they are all examples of Corporate Sponsored Superheroes, so do their bosses/sponsors. Also Wild Tiger/Kotetsu T. Kaburagi winds up being known to the general public when it becomes the only way to clear his civilian name to is to go public given the time frame he was working under.
Horimiya has Miyamura pretend to be Konoha, Hori's cousin, when his Bishounen self interacts with Yuki, Hori's best friend.
Nurse Angel Ririka SOSzigzags this. The Magical Girl Warrior heroine keeps her world-saving activities secret from her friends and family. But she's not really trying to hide her identity from the villains; she even transforms in front of them. And for their part, the villains know where she lives and they try to exploit her civilian identity. They just don't do it very well.
Haiyore! Nyarko-san beats this trope up for its lunch money like it does so many others. Though the alien characters will try to keep Muggles from seeing their battles with Cosmic Horrors, they do little else to maintain The Masquerade. Nyarko will gladly introduce herself as "The Crawling Chaos who creeps up on you with a smile, Nyarlathotep", and when joining Mahiro's high school gave a speech where she outright says she travels the stars and fights Malign Deities. And it's not even a case of being written off as a Cloud Cuckoolander, since people always seem to believe her Blatant Lies about being pregnant with Mahiro's child.
Several characters in Attack on Titan have secret identities. Most play it absolutely straight, maintaining them for variousreasons. However, one turns out to be a Deconstruction: Reiner Braun is unable to handle the guilt of his crimes as The Mole, and slowly loses focus of his true self. This causes him to suffer bouts of Trauma-Induced Amnesia, repressing his real memories while completely submerged into his false identity.
J'onn J'onzz, the Martian Manhunter, originally masqueraded as a human police detective named John Jones; a later Retcon made this an impersonation of a real detective Jones whose killing he had witnessed. Stories in the Modern Age have established the idea that, as an unlimited shapeshifter, J'onn has actually created dozens of secret identities (and at least one other heroic identity, the Bronze Wraith).
Thoroughly deconstructed in the Post-CrisisCaptain Atom, in that Cap had a "secret non-identity": a government-written cover identity of "Cameron Scott" that existed only on paper, to hide his origins as the time-displaced product of a 1960s military experiment, and to hide that Cap was a government agent masquerading as a superhero.
The deconstruction of the secret identity trope and its moral and ethical implications was one of the major themes of the series.
Trident, an opponent of the New Teen Titans, was actually three separate individuals masquerading as a single villain.
Similarly, the Crimson Fox of Justice League Europe was actually a pair of twin sisters sharing both a single heroic and civilian identity (after having faked the death of one sister).
Oliver Queen, Green Arrow, says in The Longbow Hunters, "All those years of maintaining a secret identity, and the only reason nobody ever found out was that nobody cared!?"
His successor Connor Hawke never even bothered; at one point he took over ownership of an apartment building and was refused insurance because he was a superhero.
Aztek introduced two background characters, a married superhero couple, neither of whom knew the other's secret identity. Think about it.
Blue Beetle: "Is it lame that I'm still excited about having a secret identity?"
One JLA storyline had an alien device accidentally split the League into two beings, one for their civilian and heroic identities each. Some of the League, especially the Martian Manhunter, hoped to leave things at that. However, it turned out that the separation only made things worse for most of them: for example, Bruce Wayne was all bottled fury with no outlet, while Batman was completely directionless. Eventually, the civilian identities had to fight the aliens who created the device, who turned out to have loosed it on purpose as a form of field test.
For the bulk of his career, Tony Stark presented Iron Man to the public as an employee wearing the armor he invented, and serving as his bodyguard. This twist would actually seem to negate a great deal of the usual justifications for bothering to maintain a dual identity — the general public knows Stark designed the armor, and any enemies of Iron Man are likely to become enemies of Stark by association. It sometimes seems the primary reason for this posture is to give Tony a measure of legal cover for Iron Man's activities — and indeed, on at least one occasion, Tony has publicly "fired" Iron Man in response to a scandal arising from his actions.
Eventually, Tony came out as Iron Man as part of a wave of secret identity refutations (Steve Rogers, a.k.a. Captain America, did the same thing around the same time).
It turns out he did have good reason for worrying about the legal cover. During the Winter Soldier debacle, he had to deny assistance to Captain America and The Falcon, since the villain's employer was one of Stark's direct business rivals. He explained that he could lose his company and end up in jail if it looked like he was using the Iron Man armor to intimidate his competitors.
Spider-Man's secret identity as Peter Parker was one of the best-kept in the business for forty real-world years. At least until the Civil War, where Tony Stark coerced Peter (who did not want any legal trouble on his back, so he had sided with him) to reveal his secret identity on live television. Then Spidey defected to the Anti-Reg movement, Aunt May got shot in an attempt on his life and the and struck a deal with Mephisto to keep her alive, with the plus of everyone forgetting that Spider-Man and Peter Parker are one and the same.
In Ultimate Spider-Man, on the other hand, Spidey's identity is the worst kept secret in superherodom. He's been unmasked by at least as many people as he's deliberately revealed his identity to. (A trend continued in the movies — he couldn't make it past his second film without being unmasked in front of literally dozens of people, although none of them recognized him.) The Ultimate version in particular may be a reference to the fan meme that Spider-Man was one of the last big Marvel Characters to even bother with a secret identity, as his Rogues Gallery was full of people who knew him personally.
And by now, on Earth-616, only the Fantastic Four, his fellow Avengers and his clone Kaine know who Spider-Man is under the mask.
The Scourge of the Underworld was an entire conspiracy collectively posing as a single vigilante killer.
Aversion: when the Fantastic Four were created, they intentionally avoided many genre tropes to distance themselves from their Distinguished Competition (that is, DC's Justice League of America) - with the most significant of these decisions being their lack of dual identities. One popular in-story explanation implies Reed does so to not make the others, especially Ben Grimm (for whom keeping a secret identity is basically impossible), feel ashamed of their abilities.
Of course, considering that the FF were heavily modeled on DC's Challengers of the Unknown, the lack of secret IDs isn't really surprising.
In one early storyline, Johnny "Human Torch" Storm attempts to pull off a secret identity. It lasts less than an issue, before he remembers that he was already a celebrity and thus it's pointless.
Also averted most of the time for Doctor Strange. Played with somewhat in that the public rarely takes him seriously — they tend to see him as just another bit of Greenwich Village color.
For a time (after he had been attacked by proxy), he had a different appearance as "Doctor Strange" and lived under a Cosmic Retcon which gave him a civilian persona named "Stephen Sanders." He eventually stopped bothering with the double life and practiced magic openly.
Possible subverted in Daredevil. there the hero was publicly outed, so the entire world knows who he is...but no one can prove it.
Bruce Banner is the Incredible Hulk, which starts off as a secret but ends up as public knowledge in most continuities, in part because it's kind of a hard secret to keep under wraps. Ditto for his cousin Jennifer Walters, AKA She-Hulk, albeit for somewhat different reasons. (Most of the time, She-Hulk is in control of whether she appears as Walters or She-Hulk; for a while, she appeared as She-Hulk pretty much all of the time, and once became locked in that form (a development that didn't bother her in the least).)
Interestingly enough, there was a period/continuity where Hulk's identity was secret from himself. Banner always knew he was the Hulk, but Hulk didn't know that he was Banner. Which kind of put a damper on his plans to kill Banner.
Thor's second identity for many years was protected by a Transformation Sequence. When Odin removed this power, Thor merely dressed normally to construct a new identity. While he worked in construction, the boss noticed his strength and his dexterity and concluded he had to be — Spider-Man. A rare subversion of the "guess is always right." (He invited him home, and one of his children looked in Thor's duffel bag; the hammer gave it away.)
Spoofed in Thor: The Mighty Avenger. After Brian Braddock/Captain Britain pretends to go to the bathroom so he can deal with a disgruntled Thor, the following conversation occurs between his drinking buddies.
Celine: Do you think we should check on [Brian]? He has been in the loo for a long time, no?
Alan: Mmm? No, it's okay. He's Captain Britain.
Alan: He's Captain Britain. He thinks his friends don't know, but he's terrible at keeping it a secret, so we pretend we don't notice. Another one?
Celine: Uhh...Yes. A pint, thank you.
Totally averted by The Punisher, as his Frank Castle identity is public knowledge. And yet, he can still regularly just walk down the street so long as he's not openly brandishing weapons or wearing his trademark skull.
In Welcome Back, Frank, Castle once overhears a plot to assassinate The Punisher in a restaurant as he is sitting a few tables over from the plotters. His Paper-Thin Disguise is...a baseball cap. But he has also hired a prostitute to pretend to be his "date," which probably did much more to throw off any idea that he was The Punisher (he also sat with his back to his target).
Subverted in one of the Black Knight's old spotlight issues. After getting arrested by some pushy and jerkass police due to a mixup (ironically he got mistaken for a supervillain that was similarly Arthurian-knightly-themed), Whitman raises a big fuss about how it's illegal for the policemen to unmask him since he's an Avenger. Later, we find out he freely tells everyone that Dane Whitman's address is where the Black Knight stays when he's in town. When Miss Bentley points out the flimsiness of this cover story compared to his fuss at the police station, he admits he doesn't actually care about his secret identity, he just "hates being pushed around".
In Preacher there is a villainous example where a serial killer called the Reaver Cleaver is hiding behind a civilian guise, a reporter investigating the serial killer's identity.
Inverted in Jon Sable, Freelance in that Sable is publically known as a mercenary. What he keeps secret is that writes children's books under the name "B.B. Flemm", and he has an elaborate disguise he wears when he has to make public appearances as Flemm. Furthermore, his publisher knows about Sable's real life, but is very persuasive in making him keep to his writing contract in that false identity.
Watchmen's Rorschach has an identity is so secret, even his colleagues don't know his real name or what he looks like under the mask for a long time.
One old comic had a one eyed army veteran who became a superhero. Forgetting his name, let's call him Mr. Anger. He retired as a Captain. His superhero name? Captain Anger. No one manages to figure out who this mysterious one eyed "Captain Anger" secretly is. Not even his friends.
Argentinian super heroine Cyber Six disguises herself as a man in her secret identity.
Orient Men, originally a superhero parody, is mentioned in the first panel of the first comic to be the secret identity of a random white collar schmuck. This never comes up again.
Savage Dragon doesn't even remember his real name so his legal name is really Dragon. Obviously, even if he wanted to keep his identity a secret, it's a bit hard since he's a big green man with a fin on his head.
In All Fall Down, Siphon's identity is not public knowledge, but her role as the world's last superhero leaves her very little time for a double life.
In Iron Hans and a fair number of its variants, the hero appears as a Knight in Shining Armor during the war, while working in a menial position — first a scullion, and then demoted to a gardener's boy — at the king's court
In The Golden Crab,the king tries to have The Tourney to substitute a bridegroom for the crab his daughter married. Three times the crab-husband shows up in human guise to fight.
In the Darkwing Duck fanfiction Negaverse Chronicles, Megavolt is the only member of the Friendly Four who actually needs one since he's the only one with any family members who might be vulnerable (and Negaduck has promised to kill anyone close to him). However, as he pointed out, "Elmo, Billy, Bud and Reginald just doesn't sound as cool as Megavolt, Quackerjack, Liquidator and Doctor Bushroot"
In the film version of Mystery Men, famous superhero Captain Amazing has Clark Kent glasses (which fool just about everyone except the protagonist), and the Mystery Men themselves. The Shoveller is open with his family though. The Blue Rajah is initially embarrassed and doesn't want his mother to think he's weird, but when he gets caught pilfering her silverware, he comes out of the closet and she turns out to be really proud of it. The scene is treated like a gay man coming out to his mother.
Iron Man: S.H.I.E.L.D. forged a cover story to explain away Iron Man's identity, Stane's disappearance, and the explosion at the Stark Industries factory. What really happened is that Stane knew all along who was underneath the armor (he hired the terrorists who took Tony hostage and gave him the reason to build the first armor, after all) and took steps to eliminate himto gain control over Stark Industries until Tony and Pepper killed him by overloading the factory's arc reactor. At the press conference where the cover story should have been fed to the media, Tony paused then simply stated, "I am Iron Man."
In the second film, not only does everyone around the world know about Tony, but Justin Hammer loudly announces War Machine's identity during the armor's showcase. Justified in that the War Machine armor is an advanced military prototypenote it's really Tony's second Iron Man armor retrofitted by Hammer created by a civilian defense contractor and piloted by a United States Air Force officer, so keeping the operator's identity a secret isn't necessary.
Black Widow has an alias, as fitting a government spy, but there is no proper secret identity. She is not even called "Black Widow" in the film.
Thor goes by his real name and never hides who he is and where he is from, which prompts most people to simply think he is insane. His friends briefly give him an alias to fool SHIELD agents... but it doesn't work. By the end, it's no secret to anyone what his true nature is.
As mentioned above the Hulk can't really keep a secret identity. Bruce Banner creates aliases only because he is a wanted man. He freely reveals the Hulk to anyone whom he believes can help. He also had no fear in forcing himself to transform in the middle of Harlem.
Hawkeye is in the same category as Captain America and Black Widow. As a government agent, he doesn't need a secret identity and is more often referred to as "Barton" or "Clint" than his codename.
Even Captain America doesn't have one. While the army kept the Super Soldier Program a secret for obvious reasons, Steve was making movies and doing USO tours. Sure, it was a cover, but Steve was still walking around without his mask backstage in full view of civilians. In fact, he was maskless in his first few adventures, going so far as to face the Big Bad for the first time without hiding his identity. He worked closely with at least one civilian scientists and drafted soldiers who would be out of the army soon and returning to civilian life. By the time Captain America: The Winter Soldier rolls around, the entire public knows who he is thanks to an exhibit at the Smithsonian detailing his entire WW2 career.
The Falcon doesn't have a secret identity in Captain America: The Winter Soldier, with "Exo-7 Falcon" being the name of the winged military exoskeleton he uses. He's pretty consistently referred to by his real name, Sam Wilson, but gets called Falcon once near the end of the movie. Like the War Machine example, a secret identity is unnecessary since Sam is an ex-Air Force officer rather than a costumed vigilante.
In the Vorkosigan Saga: Brothers in Arms novel by Lois McMaster Bujold, Miles Vorkosigan, after being ambushed at a party, tries to distance himself from his Secret Identity Admiral Naismith by claiming Naismith is his clone. Then he finds out that he really does have a clone, who tries to impersonate him and is not spotted by Miles's friends because they think the clone story is a fabrication. Naismith's friends and men, however, believe in the story. A few years later, in Mirror Dance, Mark uses the info to pretend to be Naismith, to pursue a vendetta. By the time it's all sorted out, the situation has gone all to hell. In Miles' case, nearly literally.
In the novel Death Wish and its sequel Death Sentence by Brian Garfield, Paul Benjamin (given the surname Kersey in the films) went to elaborate lengths to maintain his dual identity as the vigilante. He knew quite well that the police would object to his sudden justice (the same reason that the Shadow and the Spider had dual identities). In the second novel, Benjamin buys goggles, a fake mustache, and a fur cap to disguise himself.
The film series of Death Wish somewhat muddies this, since movie producers often demand that expensive name actors make their face completely visible, since they pay so much for them. However, the makers of the films did not completely ignore that Kersey had a dual identity. In the second film Paul Kersey buys an old pea coat, gloves, longshoreman's cap, and beat up pair of pants while prowling around as a vigilante. He rents a room in a flophouse to do first aid for his injuries. In the fourth film, the LAPD did not know the vigilante's identity. Also in that film, a man blackmails Paul Kersey into a meeting by announcing to him that he knew of his activities as the vigilante and would expose him.
The Penetrator, from a series of novels published by Pinnacle in the 1970's and 1980's, maintained a dual identity as Mark Hardin. Since he had served in the military, he quickly realized that his fingerprints remained on file and would betray. Therefore, he developed special flesh colored prosthetics to prevent them from betraying him.
Richard Stark's thief character Parker used the alternate identity of Charles Willis to launder his gains from his heists, owning parking lots and gas stations for tax reporting purposes. (Stark, himself, had a "secret identity": he was a pseudonym used by Donald E. Westlake.)
Similarly, Max Allan Collins' Nolan owned various small businesses whose juggled books hid his swag and boodle.
Leslie Charteris' the Saint's true name remained unknown to the public until the end of the book The Last Hero. As the Saint would later reminisce on page 140 of Count on the Saint (hardcover edition), the public knew of him at first as only "an avenging wraith". When Templar attempts to stop warfare in The Last Hero, the authorities became aware of him. However, in later stories such as The Sleepless Knight, the Appalling Politician, and The Melancholy Journey of Mr. Teal, the Saint and his associates would wear masks as needed after the Saint made an understanding with Inspector Teal.
Many paperback original series featured protagonists who operated as "mystery men" without the public knowing their true identities. These include the Hitman (Mike Ross), the Hitman (Dirk Spencer), Hawker, the Sharpshooter (Johnny Rock), the Avenger (Matthew Hawke), the Marksman (Philip Magellan), the Assassin (Peter McCurtin series), the Revenger, the Revenger (yet another series), the Protector (Alex Dartagnan), .357 Vigilante, Cross (Andrew Vachss series), the Vigilante (V.J. Santiago series) and Chant.
The Gray Seal, by Frank L. Packard. Jimmy Dale as the Gray Seal also used various alternate identities such as Larry the Bat, the forerunner of the Spider's second alter ego of Blinky McQuade.
Arthur Rosenfeld's Xenon Pearl's identity as a mob fighter remains officially unproven on police record, at least in the first novel.
John Mannering, the Baron, in the early novels by John Creasey.
In Wearing the Cape, secret identities are optional and a lot of superheroes don't bother with them. Some have undergone physical transformations that make secret identities impossible, but many also had public breakthroughs that "outed" them from the start. One variation on traditional secret identities is a legal second identity, established with the help of the government, much like that of witnesses in the Witness Protection Program.
In the Chivalric RomanceRoswall and Lillian, Roswall magically appears as an armored knight to fight in The Tourney for three days, despite working as a menial servant in between. (Having given The Promise not to reveal his true identity, he had no other means of support.)
Similarly in Gowther and Robert The Devil (as The Jester) — though in their cases, this was an act of penance for their diabolical behavior.
The missing Princess Halley of A Brother's Price went by Cira to investigate the people who bombed a theater without drawing attention. When helping Jerin she did not tell him her true identity, at first because he wouldn't believe anything she had to say. They were in sketchy circumstances.
Codex Alera features Tavi, a boy from the rural and remote Calderon Valley, who is just a simple shepherd boy right? Wrong! He's actually Gaius Octavian, son of the dead Princeps, grandson of the First Lord and heir to the throne.
In Ivanhoe, the titular Wilfred Ivanhoe makes his first appearance at a tourney as "The Disinherited Knight", and his identity is not revealed until later when some knights loyal to Prince John attack him. Also at that tourney is a mysterious archer named Locksley, who is actually Robin Hood.
Zigzagged in The Dresden Files: Harry makes no secret of the fact that he's a wizard (he's in the phone book, under "Wizard"), but there are some things about the wizarding world that he's not supposed to share with mundanes. When he inevitably does, they become a Secret Keeper. Later in the series, he establishes The Grey Council, which is more functionally a secret society, but the principle is the same.
There's an entire chapter devoted to this in How To Be A Superhero. The authors' recommendations for best secret identities include millionaire playboy (so you can leverage Crimefighting with Cash) and a politician (as you can disappear at any time without accountability).
Superhero: "I just gotta go out for a quick blow job and score some crack, OK?" Aide: "Sure thing, Senator!"
In Legacy The Tale Of The American Eagle, this is a huge plot point for American Eagle aka, Nathan Wagner. He only revealed it to his closest friends, to the point where he has filed a false identity with the government's Department of Justice and Department of Metahuman Affairs (hugely illegal, and implied to both threaten the sentences of any criminals he put away, and have a team of Cape Busters come after him), to prevent them from getting tempted to stick their nose into his family's charity. Once he goes on the crusade, the government puts more than a cursory effort into checking his paperwork, and finds out that the man on their paper doesn't exist, then reveals to the world that the manager of a charitable foundation is a superhero.
Live Action TV
Parodied in the Monty Python's Flying Circus sketch "Bicycle Repair Man", which is about a man in a society of Supermen who, when bicycle-related trouble arises, becomes the overalls-and-cap wearing Bicycle Repair Man. "Is it a stockbroker?" "Is it a quantity surveyor?" "Is it a church warden?"
In the first few seasons of Power Rangers, all the heroes maintained "secret identities," even though all the villains knew full well who they were (and often attacked them as they went about their civilian lives). Since then, most seasons keep up the tradition, with several finales where the group is found out or where they deliberately morph in public. A few seasons, however, do away with this and let themselves be publicly known, due to the Rangers also functioning as a public law enforcement or rescue service.
Super Sentai rarely bothers with Secret Identities except when the Rangers are still in school such as Turboranger or Megaranger, and this is solely to prevent alienating them from their peers at school Boukenger plays this straight (in early episode a least) and Goseiger plays this straight as well with The V cinema special revolving around their Identities becoming public knowledge. Otherwise the teams are either military sponsored with the members belonging to the military (Goranger, JAKQ, Changeman, Maskman, Ohranger, etc), the teams abandon their civilian lives after becoming Rangers and live and operate solely out of the team's base (Bioman & Liveman), or the teams are not from Earth and have no civilian lives at all, and operate out of their bases (Flashman, Zyuranger & Gingaman).
Kyoryuger is worth special mention. After their first battle together, Daigo immediately de-transforms and gladly introduces himself, but the other four refuse to do likewise, making this a rare internal secret identity case. However, in short order Daigo's magnetic personality inspires the others to open up to each other and start working as a real team.
On The Vampire Diaries, this was Stefan in the beginning. He kept his secret that he was a vampire from others and tried to pass himself off as a regular high school student.
As befits the nature of the show, Who Wants to Be a Superhero? requires that the contestants guard their secret identities at all times. Letting hers slip got Monkey Woman eliminated in the first season; in the second, Hyper-Strike was reprimanded for telling his real last name to a group of children, and only survived that round of eliminations because fellow contestant Parthenon botched the Secret Test of Character at the same time.
Dexter Morgan carries out his slayings of fellow, but less selective serial murderers anonymously, since he knows that his lack of normal empathy alone would land him in an asylum. Morgan's daily feigning of normal human emotions represents as careful a masquerade as Don Diego Vega and Sir Percy Blakeney's role playing as fops. He's so good at it, it starts to cause problems when he realizes that he isn't faking it...
Six Feet Under has multiple minor ones. David hides that he is gay. Nate hides the fact that he was diagnosed with AVM.
Zorro, of course. Like the Scarlet Pimpernel and Superman (in his earlier incarnations), Zorro maintains an alter ego who behaves like a bumbling coward.
In the British kids' series Help Im A Teenage Outlaw, the main characters Tom, Moses and Deedee are secretly the highwayman Swiftnik and his two sidekicks. However, unknown to the other two, supposed peasant girl Deedee is actually an identity used by Lady Devereaux, a Rebellious Princess whom Tom/Swiftnik thinks of as his true love, despite being incapable of recognising her without her wig and dress.
Maid Marian on the latest series of Robin Hood runs around Nottingham distributing food and medicines as the Night Watchman. No one manages to figure this out.
Amanda Clarke on Revenge uses the alias of Emily Thorne (which she gained from exchanging identities with her juvie cellmate) in order to infiltrate the Hamptons and take down the people who destroyed her life without them recognizing her.
Buffy the Vampire Slayer. As lampshaded below in "What's My Line", Buffy has a slight problem with this concept, swiftly gathering a small circle of friends who know her identity as the Slayer and help Buffy in fighting evil. By the end of season three it becomes obvious that despite Sunnydale Syndrome the entire school has a rough idea of what Buffy does, and they give her the Class Protector Award.
Kendra: And dose two, dey also know you are de Slayer?
Kendra: Did anyone explain to you what 'secret identity' means?
Many fictionalisations of Spring-Heeled Jack, such as written by Burrage. Note that the real sightings happened in 1886.
WWEwrestler/parody superhero The Hurricane, true to form, maintained a secret identity as mild-mannered backstage interviewer Gregory Helms. His costume as an interviewer was even more outlandish than his superhero costume, with big thick horn-rimmed glasses and a plaid fedora with a press pass sticking out of it, and he fooled absolutely nobody.
Except for the occasional character given an Idiot Ball by the writers.
He's since ditched the overdone getup for a simple suit and ponytail, though the Idiot Ball returned in full force. Especially notable in the fact that he's billed as Hurricane Helms and sports the sleeveless Badass Longcoat Helms wore after ditching the gimmick the first time, yet has been given two separate profiles on their website!
City of Heroes recently added the Patrol feature, which grants a double XP bonus for time spent logged out. It's supposed to be as if the character has switched roles and is doing a civilian job.
And logging out in certain locations grants other bonuses, the Train Station bonus is a speed boost, the Graveyard bonus is Debt protection, etc.
Subverted in the webcomic Everyday Heroes. The main character, Mr. Mighty, wears his superhero outfit all the time, even when doing yard work and chatting with the neighbors.
Spinnerette wears a costume all the time. Her heroine costume is a form-fitting leotard, mask and wig that depicts her as a lithe, long-haired brunette with 6 arms. Her civilian costume is a bodysuit under bulky clothes that depicts her as a chubby, bookish, short-haired blonde with 2 arms. Interestingly, her boss, friends, etc never ask about the sudden drastic weight-gain.
Tower of God: Because he is officially dead and is supposed to stay that way, 25th Baam, a shiny-eyed, short-haired, meek but adorable guy goes by the name Jyu Viole Grace, a silent, strong badass who looks a lot like a woman with that long hair which also hides his face.
In El Goonish Shive, Elliot's superheroine spell has three alternate civilian alter ego forms (each with distinctive built-in personalities and clothes) in addition to his normal form which is is his primary identity. This gives him the ability to have a Multilayer Façade.
Let's not forget that if you've read the webcomic, there's also a Rival to consider.
Let's not even drag in any knowledge you'd gain by visiting the forums.
Secret identities are a big deal throughout the Whateley Universe. At the Superhero School Whateley Academy, students use codenames, and for anything that might expose them (like printed campus security reports or the televised combat finals) they have to go by the codename and wear a costume. Way back when the headmistress was Ms. Might and her secret identity was blown, her husband was murdered and her kids were terrorized. She's tough on this rule
Lots end up using their codename more than their real name. It's supposed to be to protect the kids' families.
Most superheroes and supervillians in Worm have one, though one group, the New Wave, attempts to go without. There's an unwritten rule that you don't try to expose someone else's identity, since someone without a secret identity has no way to retire and nothing to lose.
Taken for a spin in the final storyline of Justice League when, pursued by the conquering Thanagarians, the Justice League members decide the safest way to move is in their civilian identities (for the members who have them). The Flash balks at the idea, since it's, you know, his secret identity, and it's not like he doesn't trust the others, but... Impatient, Batman simply rattles off everyone's real name, finishing with his own.
Of course, by that point, "everyone" was just himself, Clark and Wally (finally confirming that The Flash of this series was Wally West). None of the others had secret identities. Clark, J'onn, Shayera and Diana all knew Bruce's, and Bruce, J'onn and presumably Shayera knew Clark's.
Green Lantern John Stewart, didn't really see the need to hide his status as a galactic cop. Even his landlady knows about it (and, in one episode, attacks Flash with a broom when she mistakes him for part of his Rogues Gallery).
J'onn preferred being in alien/human hybrid form, and didn't hide it. But if he wanted to, he could be anyone (and eventually used this when he took a break from the league).
Shayera had wings, and would have trouble hiding her identity. A tie-in comic showed her using a backpack to hide her wings; how practical folding them like that was not discussed.
The show flip-flopped on just how established Diana was, but her identity was never a secret; it was her super-persona that was a secret from her family.
Another one from the DCAU: the Mystery of the Batwoman film features three separate women taking on the Batwoman identity, one at a time, to get back at the mobsters of Gotham City (having in mind that one of these girls is the daughter of one of said mobsters).
Transformers played with it a bit, putting what was, at the time, a new twist on it... The secret identities weren't millionaire playboys or mild-mannered reporters, but cars, jets, cameras, and other everyday vehicles and objects.
The titular hero of Danny Phantom has this big-time. The only people who know his secret identity are his two best friends and his sister (along with every villain and ghost he's ever met). The show plays a lot with the idea of "what if ____ knew about his powers?" Although that might be because it's heavily influenced by Spider-Man. Though one has to ask how people couldn't figure it out, as his real name sounds pretty much exactly like his secret identity name.
The show Randy Cunningham9th Grade Ninja centers around the Norrisville ninja who is in fact Randy Cunningham. He keeps his identity a secret to stay save from his enemies. He only told his best friend Howard Weinerman about his secret identity, though several others have come to know it.
Averted in Winx Club season 4 where they show themselves as fairies to the people of Earth, but don't have secret identities and they're known by everyone, especially to the likes of a game show host, an Intrepid Reporter, and Bloom's Earth rival Mitzi.
Kilowag:(to Shyir Rev and Biata)That thing on his face? It's a mask. He wears it in case some Earthling sneaks onto the Interceptor—while we're in space, mind you—and goes, "Aha! The Green Lantern on my planet is Hal Jordan! I'm telling everyone!"
In Young Justice, almost the entire Team have secret identities for "civilian" life. The only one without one was Aqualad, who was perfectly well known as the king's protege in Atlantis. M'gann and Conner's identities (Meghan Morse and Conner Kent) were known to the other members of the team, while Robin (Dick Grayson) and Kid Flash (Wally West) were the only one to know each other's identity. Artemis' (Artemis Crock) identity is technically unknown to her teammates, but Robin and Red Arrow (Roy Harper) both deduce it, with Robin having fun in several different episodes by toying with her story.
Truth In Television
Undercover Police Officers obviously cannot use their real identity (i.e. a cop) to infiltrate gangs and catch drug dealers, and so on.
And no, they don't have to identify themselves. Ten years of work is not going to be overturned by a technicality like that.
Similarly the addresses and phone-numbers of police officers and federal agents are somewhat protected.
Army, Airforce and Naval troops also often use codenames over the radio, and many build up reputations that earn a nickname, either for themselves (Rommel - The Desert Fox) or for their regiment.
Secret agents would obviously be useless without a false name or, at the very least, a code to identify themselves to their handlers. However, many agents with Non-Official Cover use their real name, they just don't say they're spies.
In the TV series Covert Affairs, Anne Walker, CIA Officer, is publicly known as Anne Walker, Smithsonian Employee. And it turns out the professor she went to help for in the pilot is himself a retired Officer.
Real life superheroes/crimefighters, people who actually patrol the streets and beat up criminals. Many are sanctioned by overworked local police forces. For example, the Chief of Police in Jackson, Michigan, has officially sanctioned 'Captain Jackson' and asked his police officers not to ask any of Jackson's costumed superheroes to give their real names.
Webhosting company reviewers/bloggers who do not wish to compromise their identity when reviewing services.
Similarly, restaurant reviewers, "secret shoppers" checking how store employees treat customers, and the like obviously need to avoid being identified, lest they receive special treatment that would distort the information they're getting.
British grafitti artist Banksy, to the point he managed to be nominated for an Academy Award without revealing his identity to anyone. Lord knows how they'd have handled it if he had won.