In the simplest version, the Greeks simply hide inside a object which they know the Trojans will be unable to resist picking up and taking inside their defenses. If the Trojans aren't complete idiots, subterfuge will be used to get them to accept the object—anything from disguising it as a Trojan vehicle up to a full-blown Xanatos Roulette. Common variations include hiding a well-trained animal inside the Trojan Horse, or a computer program. In Speculative Fiction the Horse itself might be a robot or shape shifter.
Whatever the details, the net result is the same. The Greeks get some of their agents inside the Trojans' walls, without the Trojans knowing they are there, which leaves the Greeks free to commit sabotage, assassinate the Trojan leader, or simply open the gate and let the rest of their friends in.
This contrasts with such tropes as Trojan Prisoner, I Surrender, Suckers, and the nailfile-in-the-cake trick, because in those cases the Trojans do know the Greeks are there, and are trying, however sloppily, to guard them. Thus, the Greeks don't usually have the degree of free rein the Trojan Horse gambit gives them.
It also contrasts with using similar tricks to smuggle inanimate objects inside the Trojan lines, typically poisons and explosives, since such objects can't make decisions. A Greek soldier, or even a well trained monkey, is adaptable. They can change plans in mid-stream, taking advantage of unexpected opportunities. Poison can't do that. Thus, a Trojan Horse allows many more narrative possibilities than do inanimate objects.
- In Dark Avengers: Ares, the title character's men do this with the bodies of two demonic horses they killed. The twist is that Travis hides in one, while the other is stuffed with explosives, so when enemies try to attack it, before another foe emerges, they get themselves blew up.
- Red Hulk used that tactic in Planet Red Hulk. He even jokes that his opponents fell for one of the oldest tricks in the book.
- In Dark Empire II, Lando and a Rebel team get to Byss (the Imperial stronghold) by hiding in war droids that the Empire had ordered.
- Dr. Brainstorm suggests doing this in Calvin and Hobbes The Series. Lampshaded by Jack.
- Troy. Well, Duh.
- Serenity film. The title ship was disguised while running the gauntlet through the Reaver ships.
- Hudson Hawk. The title character smuggles himself inside the Vatican inside a large mailed crate.
- In the Hellboy movie, Kroenen combines this with My Death Is Just the Beginning. He shuts off his heart, then BPRD carries him back to their headquarters. Then Kroenen revives on the examining table.
- Oceans Eleven
- They smuggle the acrobat into the vault inside one of the cash boxes. And then smuggle most of the team both in and out in the SWAT vehicle.
- Used twice in Thirteen. First to sneak a camera and computer connection into the baddy's office and later to get a magnetron into the computer core.
- In Monty Python and the Holy Grail, Sir Bedevere devises a slight variation to infiltrate the French castle, involving a wooden rabbit. He only gets one little detail wrong -- he forgets that there should be somebody inside it. Just as well, since the French catapulted it back out.
Bedevere: Um, l-look, if we built this large, wooden badger...
- In The Thomas Crown Affair, thieves sneak into a museum inside a greek statue of a horse (though, it isn't wooden). It's delivered as an upcoming exhibit.
- White Heat has Cody Jarrett and his gang using an empty tanker truck to smuggle themselves into a chemical plant so they can rob its payroll office. Cody lampshades this by mentioning that he got the idea from a story his mother had told him:
"Way back there was a whole army tryin' to knock over a place called Troy and gettin' nowhere fast. Couldn't even put a dent in the walls. And, uh, one mornin', one mornin' the people of Troy wake up, look over the walls and the attackin' army's disappeared. Men, boats, the works. Taken the powder. But they left one thing after them: a great big wooden horse. And, according to Ma..."
- The final ploy of the heroes of Independence Day was to send two of their men to The Mothership in a captured alien fighter to upload a virus. Went well, up until they tried to leave...
- Mom and Dad Save The World uses a giant bust of the Big Bad. The Big Bad, being an idiot like everyone else on the planet only thinks that the bust got his face wrong, and has it brought in just so people can tell the difference. This particular Trojan Horse scheme hits a little snag since the native rebels forgot to include a way out of the bust after sealing themselves inside it (again, planet of idiots).
- It doesn't actually happen in The Iliad. It's mentioned in The Odyssey, but the actual event isn't depicted in either poem, but rather in the other, lost epics of the Trojan Cycle. It is described in flashback in The Aeneid by Vergil, though. The original is far more flattering to both sides than the simple version usually taught in elementary schools. In the original, the Greeks simply cannot take Troy, try as they might, because Poseidon has placed over the city a protective veil. So they construct a great wooden image of a horse, the sacred animal of Poseidon, then except for the few men concealed within the image, withdraw from the city, beyond any range from which they could attack, with a message placed before the image that reads, "For the honour of Troy and the glory of Poseidon." The Trojans are then forced either to reject the gift, which will likely offend Poseidon who will then withdraw his protection from the city, or bring it inside, which will require them to partly dismantle the gate and thus rend the veil. Either way, the veil is down and the Greeks have at least a fighting chance to take the city. There's a reason David Xanatos is Greek.
- In the novel Beyond Varallan by S.L. Veihl, the protagonist hides warriors onboard shuttles that were supposed to be carrying refugees away from the titular planet in order to take over the enemy vessel and hand them over to the other enemy vessels in order to save their world. It's Better Than It Sounds.
- Parodied twice over in the Discworld series:
- In Eric, the Tsorteans immediately see through the ruse and surround the wooden horse with soldiers. It turns out that the Ephebian commander expected that to happen, and merely intended the horse to distract the defenders while he and his men got into the city another way.
- In Pyramids, war breaks out again between Ephebe and Tsort. Both the Ephebian and Tsortean armies build several giant wooden horses. Facing each other. The Tsortean officers get one with rockers.
Ephebian Sergeant: Look, soldier, anyone bloody stupid enough to think we're going to drag a lot of horses full of soldiers back to our city is certainly daft enough to drag ours all the way back to theirs. QED.
- Nathanael West's 1931 novel The Dream Life of Balso Snell has its protagonist encountering a variety of characters inside the actual Trojan Horse.
- Doctor Who
- In the serial "The Myth Makers", the Doctor is actually the one to suggest the idea of a giant wooden horse (after his earlier suggestion of catapults to fling the soldiers over the walls is rejected) after being captured by Odyessus during the Siege of Troy.
- Also deliberately invoked in "Underworld" and "The Armageddon Factor."
- The NCIS episode "Trojan Horse". A guy gets into the evidence locker to tamper with evidence by hiding in the stuffing of a seat of a taxi made to look like a crime scene.
- The Chaser's War on Everything attempted towing a literal Trojan horse (containing Chas dressed as a Greek soldier) into a number of secure locations. They got into a surprising number. Except for, hilariously enough, the Turkish embassy in Sydney. Troy was in what is now Turkey.
- Part of The Caper in the Farscape episode "Liars, Guns and Money" involves hiding Rigel in a cargo container then depositing the container in the bank they are intending to rob.
- Sharpe and the Chosen Men did this at least twice. Once with the youngest of their number groaning on a stretcher while the French-speaker shouted about cholera, once with Harper covered in blood from a pulled tooth and pretending to be mortally wounded until the time came to attack.
- The A-Team once used a Trojan Whiskey Delivery Truck to get inside a convent that had been taken over by South American Guerrillas (who had just run out of booze).
- On Numb3rs, a group of criminals plan to kill a prisoner who is about to turn state's evidence. Their plot involves an overly complicated scheme that first involves killing power to sections of LA to cause the prison to run their generators out of fuel. As more fuel is required, the criminals hide inside the fuel truck to plan their entry into the prison. However Fridge Logic kicks in when you realize that the tanker was empty. Apparently the prison guards fail to check the inside of the truck or even tap the side to see it is empty.
- In episode 33 of Chouriki Sentai Ohranger, "The Five Robos' Great Riot", the Ohrangers trick Bacchus Wrath into bringing the new secretly-constructed Blocker Robos inside his base by disguising them as powerful, jewel-decked blocks and presenting these as a gift. Once inside, the Ohrangers activate the robos and trash the place.
- In the CD&D adventure "Skarda's Mirror", the bandit warlord Skarda uses the title magical mirror to act out this trope, selling or giving it to his enemies so that the thousands of troops in the adjoining Pocket Dimension can bypass their defenses.
- New Super Mario Bros. Wii. the Koopa Kids kidnap Princess Peach by sneaking into her castle inside a giant cake during her birthday party.
- In Discworld Noir, Lewton sneaks on board the Milka by hiding in a crate that's being taken on board, and later discovers that a killer snuck into the Patrician's Palace by hiding in a wine barrel that was delivered there.
- In StarCraft II: Wings of Liberty the heroes storm the Dominion weapon research facility and steal a Super Prototype of a Humongous Mecha scheduled to be shipped to the Dominion capital world to lead a parade. They then have one of their own pilot the mecha and ship it to the destination, where it is used to launch a surprise attack in the middle of the parade.
- Facebook game Backyard Monsters has wild monsters deliver such a horse outside your base. They attack whether you accept the horse or sent it back.
- In the Lupin III game, Treasure of the Sorcerer King, Lupin manages to get himself on a train by hiding inside a statue that his partner delivers onto one of the cars.
- Jonny Quest TOS episode "The Robot Spy". Dr. Quest is tricked into taking the title device inside a military base.
- The Simpsons, "Lemon of Troy": To get a stolen lemon tree from a Shelbyville impound lot, Homer and others park Ned Flanders' RV in front of a hospital and wait for it to be hauled away. After the plan works, Homer comments that no one in history has ever had such a brilliant idea.
- In Time Squad, the Squad go back to the time of the original Trojan Horse, only to find that the Greeks filled the horse with candy. After a little coaching, they send in a wooden giraffe... full of little chocolate soldiers. Finally, the Greeks send over a giant wooden soldier full of horses... which run wild and wreck Troy.
- Happened once in Recess, with TJ's gang trying to recapture their fort from Lawson, by hiding in a home-made submarine.
Bully: Didn't somebody once say beware of geeks bearing gifts?
- An episode of Hey Arnold! sees Arnold and his friends attempting this inside a giant pig after losing Abner in a war reenactment competition. One of the members of the other side recognizes the trick and tries to point it out, but their leader (Rex Smythe Higgins) refuses to listen.
- Chip 'n Dale Rescue Rangers. The Rescue Rangers have an Easter basket that turns into a tank. And since Everythings Better With Pineapples, they use a hollowed-out one to spy on Fat Cat.
- Re Boot: Big Bad Megabyte once hid himself in a fake upgrade during one of his bids to take control of Mainframe's Principal Office. Oddly enough, he actually becomes a Trojan Horse virus in the last season granting him shapeshifting abilities.
- Star Wars the Clone Wars: Sabotage Droids get delivered to Coruscant under the guise of simple cleaning droids.
- Happens in the Super Mario Bros Super Show episode "Trojan Koopa". Instead of a horse, Mario, Luigi and Toad build a giant wooden statue of King Koopa himself, banking on his ego to take the bait. Adding to the trick is that earlier they grabbed two of his Troopas and sent them out to sea with a dummy to make it look like they were giving up.
- This is attempted in the Codename: Kids Next Door episode "Operation: C.A.K.E.D.-F.I.V.E." with Sector V hiding in a wooden cake, to sneak in the birthday party of the Delightful Children from Down the Lane.
- In computing, a "Trojan horse" or more simply "trojan" is a virus that disguises itself as an innocuous program and sneaks past anti-virus programs to infect computers. They don't self-replicate, but are harder to spot and can royally mess up infected computers.
- A hilarious case of Unfortunate Names: Trojan Condoms. Either they're named for the city, which had its defenses fall, or it refers to the horse, which got the city to open their defenses so they could be ravaged. Upon that last thought, perhaps Fridge Brilliance rears its head...