Impersonation Gambit

A sting operation in which the hero tries to infiltrate the villain's organization by passing themselves off as one of the bad guys.

For example, Bob is going to meet Alice to be given an evil plan to carry out. The hero, Charlie, catches up with Bob before he can meet with Alice. Since Alice and Bob has never met face to face, Charlie goes to the meeting point, pretending to be Bob. Charlie is attempting an Impersonation Gambit. If successful, he will take down Alice's organization, but this gambit doesn't always go as planned.

A subtrope of The Infiltration, only in this case, they are impersonating a real person that the villains were expecting to meet. Can result in a You Are Already Checked In if the person they're impersonating shows up. Compare Dressing as the Enemy which this trope can often overlap with.

Inexperienced in impersonation, the heroes might act according to Most Definitely Not a Villain (except that they're trying to pretend that they most definitely are a villain). They may also face the need to prove that they're as evil as the impersonatee is known to be.

Film

 * Diamonds Are Forever: James Bond impersonates Peter Franks in order to infiltrate the diamond smuggling operation.
 * Another James Bond example occurs during the opening of Die Another Day.
 * In Ultraviolet Violet impersonates a courier in order to get inside the Archminstry's headquarters and steal the weapon that will wipe out the hemophages.

Literature

 * Done in almost all possible ways (from stolen uniforms to magical transformations) in the Black Company. Gambit Pileup is the typical result.
 * The Executioner series. Mack Bolan would sometimes infiltrate Mafia organizations by masquerading as an elite hitman. He did so by displaying an ace of spades, which they used to identify themselves.
 * Done in Harald, when Mord hires Westkin mercenaries as soldiers to assassinate, who has outlived his usefulness, Harald gets his own Westkin allies to impersonate them.

Live Action TV

 * Mission Impossible. This was sometimes used in IMF operations.
 * Jack Bauer attempts this twice throughout the shows run. In both instances, a suspect is killed before Jack can get any info out of them, but Jack improvises when their phone rings, and gets a meeting location where he continues the guise.
 * Christopher Chance successfully pulls this off in "Taking Ames".
 * In another episode, to protect a woman he believed was being targeted, he posed as online date. However, the real date shows up, blowing Chances cover. The "real date" is revealed to be the assassin hired to kill the woman, but luckly, Chance saves her.
 * Chuck pulls this off in "Chuck vs the Fake Name" by taking an assassins indentity to find out who the ring wants to kill.
 * There was a similar plot in Monk. Even more coincidental since one of the mobsters was played by the same actor who played a mobster in the that episode of Chuck.
 * Angel pulls one of these in the Season 2 episode "The Shroud of Rahmon," impersonating a hip Vegas vampire to infiltrate a group of thieves.
 * Villain example in Heroes. Sylar kills Zane Taylor, steals his power, and passes himself off as him to Mohinder.
 * NCIS - Tony and Ziva pose as an assassin couple in order to sniff out who they were taking orders from.
 * Happened in an episode of the new Knight Rider.
 * In Jake 2.0, Jake infiltrates a meeting of a group of hackers (who had previously only communicated online) by impersonating a group member who has been arrested by the NSA.
 * The Cape: Vince poses as the bomber Razer as a way to spy on Scales.
 * On Charmed, an assassin tries to kill the sisters, only to be killed by Prue. She then impersonates the assassin to meet her client, who had apparently never met the assassin in person before.
 * In one episode of Starsky and Hutch, Hutch impersonates a reclusive hitman who has just been taken into custody. This goes wrong when the hitman escapes and shows up at the meeting...

Video Games

 * In Metal Gear Solid 3: Snake Eater,.
 * Also in Snake Eater, Snake impersonates Major Raikov in order to get to the west wing of Grozni Grad.

Web Comics

 * Rather humorously averted in Double K - having just raided a drug dealer's warehouse, Kamina notices the suspect's portable phone ringing and answers it. When the guy on the other end assumes that he's talking to the dealer as normal, well... in the author's own words, "True to form, Kamina immediately pisses away any usefulness this development may have brought." Explosions ensue.

Western Animation

 * Gloriously played in the Batman: The Animated Series episode "Almost Got 'Im", where, of all people, turns out to have been Batman the whole time.

Real Life

 * Two FBI agents were able to stop a bomb plot in Portland by impersonating the would-be bombers' online contacts.