The World's Expert on Getting Killed

They know more about the threat than anyone. Can tell the hero / heroine everything they want to know. They're a cop who's been hunting the Serial Killer for their entire career, or the Great White Hunter who knows more about dangerous animals than anyone. Perhaps they're an expert on ancient curses, or is schooled in the ways of killer robots. Whoever they are, they're the good guy's best and most reliable source of information regarding The Threat, its plans, its motivations, its patterns, its strengths, and its weaknesses.

Unfortunately for them, they're not the hero of the story. Even more unfortunately, they're just useful enough to the hero that their death will make our heroes even more vulnerable, and their plight more dramatic. Worse still, since they're the expert on The Threat, their death by the Threat will augment the advantage the villain has over the heroes -- after all, if this Expert couldn't win against them, what shot do our non-Expert main heroes have?

The above may be unfortunate, but this is just embarrassing: Not only will our Expert get killed by the Big Bad, but at no time in the confrontation will our Expert even pose a major challenge to the Big Bad. The Expert, (usually late in the game having imparted all their useful advice and wisdom about the threat), will be dispatched neatly, cleanly and almost effortlessly by the villain/monster/demon, making the audience wonder how in the hell this guy even lived long enough to ever become an expert on this particular threat at all.

The two important criteria are that this supporting good guy:
 * 1) has superior knowledge/training/exposure to the Threat, enough that they can educate the Real Heroes about it, and
 * 2) when actually confronted with the Threat, they go down fast and put up a perplexingly feeble fight.

Always keep in mind the second one. If our ill-fated supporting hero took out a couple dozen mooks, held their own (but then lost) a knock-down drag out fight, put three barrels in the shark before being eaten, or otherwise put up a decent fight before dying, they do not fit this trope.

Compare/contrast The Obi-Wan, who is also wise to the threat and often killed by it nonetheless, but The Obi-Wan's death, if and when it comes, is often a Moment of Awesome, Obi-Wan Moment, or at least dramatic. Compare also The Worf Effect, which is where an enemy dispatches a more generally established badass with ease, rather than one specialized against them. Finally, consider Mentor Occupational Hazard, which is the tendency of mentors to the hero to die.

Anime

 * In the first season finale of Blood Plus, Saya, Haji and Eric team up with a squad of professional chiropteran (vampire) hunters. They die to a man fighting baby chiropterans.
 * In Fullmetal Alchemist, Lieutenant Colonel Hughes upon working out the secret plan of the Big Bad and running out to inform his superior Col. Mustang, is attacked by two main enemies who work for the Big Bad. He fights back, but in vain and is killed without relaying any of the info. This then adds to the plight of the hero's and makes it personal.
 * The Anti-BM unit in Bio Meat gets eaten mere moments after reaching the infested building. Would it hurt them to put those fancy suits on BEFORE leaving the chopper?
 * Puella Magi Madoka Magica: Mami Tomoe is a veteran Magical Girl who introduces Madoka and Sayaka to the risks and rewards involved so they can decide if they want to enlist. She gets eaten by episode three's Monster of the Week.
 * The protagonist who truly knows the most about the dangers Magical Girls face, Homura, is actually a subversion. She's the only character who not only survives the series, but never dies in any of the shown timelines.

Film

 * Robert Muldoon from Jurassic Park "knows more about Raptors than anyone" ... but is pretty quickly and easily dispatched by the raptors once they're loose when they use their standard attack pattern. One wonders if the fact he was a hunter in a Hollywood movie might have something to do with it. In the book, it's Hammond instead, and Muldoon survives the experience after shooting the T-Rex with a rocket launcher, blowing at least one raptor in half with a shotgun and still continuing to be an untouchable Badass even after he finally gets so drunk he can barely stand.
 * Muldoon does have one thing in his defense: He's a hunter, not a paleontologist. He's studied the Hammond-mutated Raptors and how they reacted in captivity, but he hasn't studied their behavior in the wild.
 * Dr. Henry Wu, who should theoretically know as much as Muldoon about the creatures he helped to create, also gets it in the book. To be fair, he was holding the Idiot Ball at the time.
 * Ian Malcolm being the only person who knows from the start that the Park is unsafe, still goes there anyway. Just so he can be the Only Sane Man and Deadpan Snarker. Fittingly, he is killed in the book. But he survives the film and it is Ret Conned in the book sequel that Reports of My Death Were Greatly Exaggerated.
 * Carson Wells from No Country for Old Men is the character most familiar with serial killer Anton Chigurh. Chigurh doesn't even break a sweat in catching up with him.
 * Well, he did call Chigurh unstoppable. The World's Expert on an Implacable Man isn't exactly immune to bullets.
 * The un-initiated Llewelen is, however much more problematic for Chigurh.
 * Major Valentina Koslova from The Jackal is assigned to help Preston and Mulqueen track down the title assassin, bringing with her all her useful knowledge about the villain. Still, her confrontation with him doesn't last long.
 * Charles Remington in The Ghost and The Darkness is the world's authority on man-eating lions, and how to make them dead. One of the lions takes him in his sleep, it seems.
 * Repeated with the Badass hunter in Prey.
 * Phillip Fitzroyce, from the Jaws 3-D, is described as a skilled hunter and naturalist who has every confidence he can take down the killer shark that is threatening the movie's fictionalized Sea World park. He lasts about five minutes against the beast.
 * This happens in the first film as well with Quinn.
 * To some extent it's really his pride that does him in. He's been hunting and killing sharks for years, and can't quite accept that this particular one might be more than he can handle.
 * The entomologist who knows all about the killer spiders of the movie Arachnophobia goes down like a Red Shirt. Perhaps a little more acceptable than most examples because he's a scientist, not a hunter, but he still wasn't very careful despite knowing how dangerous the spiders were.
 * Four Jedi Knights set out to arrest Chancellor Palpatine/Darth Siddious in Star Wars III: Revenge of the Sith. They're led by Jedi Master Mace Windu, who had just then been warned by Aniken that Palpatine was a Sith Lord, so there's no excuse for being taken by suprise. And yet Siddius takes them by suprise. Two Jedi don't even parry a single slash from Siddious's lightsaber before immediately dying, and one more gets in a few blocks before being felled. Only Mace Windu survives long enough to offer a decent lightsaber battle. Windu is not this trope. The other three Jedi are.
 * Predator 2. Peter Keyes, the world's leading expert on the title creature, goes up against it. He manages to survive the first round but is killed later, leaving the Hero to finally dispatch it.
 * Cube has Rennes, AKA "The Wren" an expert on escaping prisons who dies in the first rooms, by having his face burned off with acid.
 * To be fair, he did have some good ideas, and made some progress. He just had no idea what he was up against.
 * Played for (dark) laughs in Feast, where "Hero", the badass-looking character who bursts onto the scene and actually seems to know what's going on, gets eaten by the creatures within seconds of his first appearance.
 * Played for laughs in Club Dread, when the battle-toughened security chief gets offed mid-speech.
 * Luca Brasi, the Corleone's top hitman in The Godfather, doesn't survive his first encounter with armed opponents.
 * Well, to be fair, this was less due to any failing on Brasi's part and much more the first real failure we see from Don Corleone, indicating that the old man is showing his years and foreshadowing his inevitable retirement and replacement, first by Sonny and finally by Michael. Corleone sent Luca into this situation without expecting to be so badly and immediately outfoxed, as he thinks he is squaring off against Tattaglia, a man Corleone has zero respect for, instead of the far more intelligent and dangerous Barzini. In fact, it is not until years later that Corleone even realizes that Barzini was his opponent all along. The Don made a bad call and lost a powerful weapon, plain and simple.
 * Justified by the story as a whole: every successful violent encounter works because it's a setup, tricking our outmaneuvering the enemy so that they are caught with their guard down. Luca Brasi's vicious brutality and existing kill count actually count for pretty much nothing, as none of the main characters except Michael really know anything about direct combat, instead playing the conflict like a game of chess. Michael himself lampshades this early on.
 * Happens in the B-Movie Alligator to its Great White Hunter. Same thing happens to an entire family of such characters in the sequel.
 * Played for Laughs in the Coneheads movie. As Dan Akroyd is about to be executed by being forced to fight a Rancor-like creature, the prisoner before him says that he's used his years of imprisonment to study footage of the creature, determine a weak spot where he can strike, and trained until he's positive he can slay the beast. When it's his turn, he goes off confidently to victory and immediately gets his head ripped off.
 * The Rage Carrie 2 combines this with Sudden Sequel Death Syndrome, killing off a Zen Survivor who tried to prevent the slaughter this time around.
 * Happens towards the end in Spy Kids 3D where a teen comes in who calls himself "The Guy". He enters the last level before the others do. You'd think a video game expert would last long, but one hit and all 100 hit points he had were GONE.
 * The ball-collecting scientist in Planet Terror is the only person in the world who knows anything about the cause of the zombie apocalypse - a green gas referred to by professionals in the business as "the shit" - and what might be done to fix everything. Guess what happens just as he's about to tell the viewers and protagonists about it.

Literature

 * Harry Potter: Book 6; Dumbledore, an expert in magic and Voldemort, gets himself cursed by making a foolish move while retrieving Voldemort's ring horcrux. Justified by the fact that, by his own admission, his desperation to find out who killed his sister (his enemy or his own misfired spell) clouded his judgement.
 * Mad-Eye Moody in Harry Potter and The Deathly Hallows. He is described as a master duelist and an expert in fighting Dark Wizards, but is killed personally by Voldemort literally five chapters into the book. He doesn't put up much of a fight before going down, either. To be fair, though, he was left in a bad position, had no way of winning the battle, and may not have had a chance to properly defend himself.
 * Avada Kedavra is unblockable, so he could only have survived if he dodged it. Considering Mundungus Fletcher disapparated, distracting him and probably throwing his broom off-balance, it's not likely he was able to.
 * Gilderoy Lockhart is a parody of this trope. He's amazing. A genius. He's defeated evil monster after evil monster- and his written works on how he did it has made him famous. Oddly enough, he seems rather hesitant to do anything in real life.

Live Action TV

 * Kendra the Vampire Slayer is introduced as Buffy the Vampire Slayer's key ally, and with skills comparable to Buffy's. When she's brought back at the end of season 2, she's dispatched by Drusilla with very little effort.
 * Jenny Calender in the same season may count as well. Her people had handled Angelus before and she was the only person who had the curse that would restore Angel's soul, thus ending the threat. Angelus kills her quite easily, leaving the rest of the Scoobies without access to the ensoulment curse.
 * On Bones the foremost expert on the serial kidnapper/killer "the Gravedigger" is killed by the Gravedigger.
 * In the X Files episode "First Person Shooter", the owner of the VR game brings in "world reknowned hacker" Daryl Musashi that even the Lone Gunman drool over like fanboys. The game AI murders him by cutting off his hands and head before he fires his first shot.
 * In Lost most of Arnst's speaking lines in his last episode are about how dangerous and volatile the aged dynamite is, so naturally he dies doing exactly what he told the others not to do with the explosives.
 * In Dexter, detectives Dokes and Lundy both serve this role, to a degree, although they are both killed by women obsessed with their respective serial killers, not the killers themselves. Additionally, Harry teaches Dexter self-preservation only to kill himself.

Video Games
"Tomasso di Viterbo: The assassin will not appear in front of you. The assassin will come out of the shadows and--
 * In Project Origin, Snake Fist/Terry Halford is your best chance of bringing down Alma. Which results in an Assassin ripping his head off seconds after you meet him.
 * In The Witcher, Raymond Maarloeve, a private eye motivated by the death of his family at the hands of the organization known as Salamandra, had amassed information on the group and its head, Azar Javed, with the hopes of bringing them down. Raymond decides to aid the protagonist, Geralt, in dismantling Salamandra. The endeavor doesn't end well for him, despite Geralt successfully defending him from Salamandra's initial backlash.
 * Spoiler:
 * In Assassin's Creed Brotherhood, one Borgia Captain claims, in Enemy Chatter you can eavesdrop on, to know how Assassins operate and thus how to deal with them, but other than being on horseback (and thus being able to flee faster), he's no harder to kill for all his bluster than any other Borgia Captains. As a result, players have been known to time their kills of him to maximize the dramatic irony. For example...

Ezio: [rushes on foot right up to Viterbo's side, pulls him leg first off of the saddle and stabs him through the throat with the Hidden Blade as he lands]"


 * Inverted in Final Fantasy X, as Auron, the party's leading expert on the Big Bad Sin, knows so much about it because
 * In Metal Gear Solid 4, the Metal Gear RAY, which was specifically built as a counter to the Metal Gear REX models being built by the other worlds, is destroyed by none other than the (half-demolished but operational) original Metal Gear REX.
 * At a closer look, though, the Ray you defeat doesn't have a tail, meaning it's probably one of the mass-produced Ray copies, not the original.
 * In Exile/Avernum 3, the first expedition to the surface is composed to hand-picked and trained members of the underworld's military and equipped with items personally made by a brilliant (if profoundly weird) archmage, and end up dead in various corners of The Empire within a few months. Your band of adventurers, with standard military equipment and limited support, save the world.
 * Not all. There is at least one who manages to stay alive and have a chat with the new guys. There might have been another, but this troper doesn't remember.

Western Animation

 * Parodied on a The Simpsons Halloween special when dolphins were plotting to recapture the land. The sea captain monologues about how he's the only one who knows how to stop them and is Killed Mid-Sentence.
 * South Park has a more unusual example with Kenny, in that getting killed almost every episode for the first few seasons has made him an expert on ways in which he might get killed. Not that that's helped him much
 * Parodied in American Dad where the helicopter carrying the CIA's top code-breaker crashes as he's arriving at the scene. Any remaining hope then falls on Scott who's "pretty good at the jumble". Scott promptly gets hit with debris flying from the helicopter.

Webcomic
>Tuck:"Lessee, Trained, experienced, competent-- I say he's dead in five minutes."
 * Lampshaded in Nip and Tuck when their Movie Within A Movie Man On The Border introduces the lead character's partner:

Web Original

 * Parodied in Gantz Abridged. When Judeau from Berserk Abridged appears to help prevent the series's disappointing Gecko Ending (having suffered such a fate in his own series), he is immediately killed.
 * Hey you bitch! I'm the strategy guide!