Sven in Voltron, sort of. He was revived in the dub.
Leomon in Digimon Tamers. Introduced in ep 21, dies in ep 34 in a way that was fairly disturbing, seeing as it was the first Killed Off for Real of a main character in Digimon, ever.
Matt from Death Note got maybe 12 panels in the manga before he gets killed. All we know is that he likes video games and is good friends with Mello.
Ukita, the member of the task force who charges off to Sakura TV and gets killed by Misa, gets more panels, but less development. His death largely serves to prove that it's possible for a death note user to kill without knowing someone's real name if in possession of the Shinigami Eyes.
Kolulu from Zatch Bell! gets defeated pretty fast, although she is still one of the most important characters since she was Zatch's inspiration and the one that made him want to win.
Not to mention this one female pilot that replaces the main character in one episode. She gets all of two scenes and five sentences of dialogue; the last one being spoken mere moments before she bites it.
All of the recruitable characters in the anime adaptation of Valkyria Chronicles. Contrast to the game where the characters have character, and you'll pull your tank and all available troops just to make sure no one dies.
In the Birdy the Mighty anime, Tute, Birdy's police partner, dies by the third episode of the first season.
In Tegami Bachi, Lily Confort is introduced, given a small backstory, suggested as another love interest for the main character... and then has her Heart eaten by a Gaichuu over the course of four chapters.
This is the fate of Acta in Black★Rock Shooter: Innocent Soul, who dies the same chapter she's introduced.
Bleach: Chojiro Sasakibe, despite being the vice-captain of Division 1, is usually relegated to a background character that does nearly nothing major. At the very beginning of Vandenreich invasion, he's abruptly killed off. His memorial is used by the Shinigami to reminisce about his in-universe reputation, which is a revelation to the audience, but it's only to set up future consequences for the Gotei 13.
Gamaran: since the series in heavily focused on battles, often with strong warriors taking down weaker ones with ease, is not uncommon to see people interesting-looking, named characters who are however quickly dispatched before we can learn more about them. This trope becomes increasingly common in the second part of the series, in the war between the Ogame School and the vast legions of the Muhou School, with many of their officers and elite warriors introduced and killed in the same chapter they appear.
Kannabi no Mikoto in Air is killed one episode after her introduction.
Many characters who die early in Legend of Galactic Heroes qualify, but the most notable among them is probably Jean Robert Lappe, Yang Wen-li's best friend since their cadet days who is reputed to be of similar calibre as Yang but has the misfortune of being assigned under an incompetent commander and is ultimately killed in action in episode 1.
The original Thunderbird, John Proudstar, died just a few issues after he was introduced in the X-Men comic books.
Serpentina, one of the characters introduced in the first issue of X-Men 2099, was killed off in the third issue. She later came back as a zombie, though.
This seems to happen to new X-teams a lot; the original lineup of the young mutant team Generation X included a character named Blink, a nervous girl with teleportation powers and pink skin. She was killed less than a month after her first appearance. Blink defied this trope, though, by proving extremely popular with fans despite her small number of appearances. So Marvel decided to bring her back... without resurrecting her. Instead, they made the Age of Apocalypse version of Blink the leader of a new team called the Exiles, which were then given their own series.
52 spends a surprising number of pages on the origins of Native American hero Superchief and then has him join up with a team of kooky side characters, only to kill him off a few issues later for basically no reason.
Saga hypes up a particularly scary villain character, then has her suddenly and unexpectedly offed by another bad guy just an issue or two later. Possibly an example of the Sacrificial Lion trope.
Mariko in Perfection Is Overrated dies in the prologue as a result of Akane's Child being destroyed, having made the entire Fuuka Academy Campus, Akane included, consider her their most important person. She is mentioned from time to time later and is also featured in the SUE-centric "A Common Enemy Without A Commmon Cause", but even there, is the first to die.
Gregorovitch the wandmaker, Bathilda Bagshot the historian, and Grindelwald the prisoner in Harry Potter and the Deathly Hallows. (Granted, Bathilda was already dead by the time we met her, whereas Grindelwald and Gregorovitch are killed by Voldemort, as seen through Harry's consciousness.)
The POV character of the prologue chapter in every book of A Song of Ice and Fire is doomed to die, and the same applies to the epilogue characters in the two books which have them. None of these characters' POV is shown anywhere else in the books, and all but two ( Varamyr Sixskins and Kevan Lannister) are pretty insignificant characters that we mostly haven't seen close-up before.
Redtail from Warrior Cats, who had a scene in the prologue of the first book and was killed offscreen a few chapters later.
Being only told from the perspective of one tribute, The Hunger Games naturally falls into this, with 13 unnamed tributes being killed in the opening bloodbath. The heroine can't dwell on their deaths, since she's being hunted herself.
In Battle Royale, four of the students (Mayumi, Izumi, Hiroshi, Ryuhei) are offed before any information about them is revealed, other than the last two being part of Kazuo's gang. Also, Fumiyo is killed before the games begin...for whispering, and their original teacher, Mr. Hayashida, was killed offscreen after protesting the Program.
Hey, look guys; It's the new GONE book! Oh, looks like they've added in a new character...Oh don't worry about it, he died in his first page. Horribly. (See Roscoe, Bette, Paint, Jasmine and Tyrell)
Percy Jackson and the Olympians Poor, poor Bianca Di Angelo. While Riordan developed her pretty well for the limited time she appeared in the third book, and she's a interesting and likable character, it was hard to really feel at a loss for someone who all you really knew is that she was Nico'ssister.
Several of the Forsaken in The Wheel of Time die before the reader gets to know them well, notably Rahvin (who hangs around for several books but appears on-page rarely and is given little backstory or motivation) and Be'lal even more so (introduced late in the third book, appears in the flesh in only one sequence and then dies although later in the series Demandred, who is extremely similar to Be'lal but about ten times as Badass, is an extremely significant villain. Subverted with Aginor and Balthamel, who are the first of the Forsaken to die after a brief fight scene in the first book- and then show up in reincarnated bodies anyway several books down the line.
24: Gave us Jack Bauer's original boss, Richard Walsh, who died in the second episode.
Alias: Renee Rienne is one of three characters introduced at the start of the fifth season, as a badass international terrorist and #8 on the CIA's most-wanted list. By the 13th episode Sydney is offering her a spot within the CIA. Naturally, she ends up with her throat cut by an even more badass international terrorist by the end of the episode
Doyle died of a heroic sacrifice midway through the first season of Angel. Joss had always wanted to have a Sacrificial Lion, though Real Life Writes the Plot was also in play due to Glenn Quinn's drug addiction. Whedon wanted to bring him back later, but Quinn died of a drug overdose in 2002.
Joss Whedon enjoys this trope. Whedon wanted to have a character be placed in the credits of the Buffy pilot, only die in that very episode. Budget constraints prevented him from doing so. This character would be Jesse, Willow and Xander's best friend since grade school. He was introduced in the first episode, in the next episode he is turned into a vampire and Xander is forced to kill him, all the while we never really got to know him or his past. And he is never mentioned again.
Are You Being Served?: Had Mr. Goldberg, an old Army acquaintance of Captain Peacock, join the staff after the retirement of Mr. Granger and Mr. Tebbs. He only lasted one season before disappearing without explanation. He had two successors, Mr. Grossman and Mr. Kline, who only lasted three episodes each before they, two, vanished from the show.
The source of the page quote; even with a spot in the opening credits Warren Keffer was not slated to live past the second season. The character was created because of Executive Meddling after the end of the first season. Straczynski never found much appeal in the idea of a Starfury ace pilot character and killed him off at the end of the second season. Reportedly, when JMS finally did get rid of the character the executives had forgotten that they had ever asked for him in the first place and did not care that their orders had been circumvented.
Two other examples from the Pilot episode of Babylon 5: Commmander Takashima, where this trope was played straight (she was replaced by Ivanova from the first season on and never heard from again) and Lyta Alexander, where the trope was subverted by replacing her with Talia Winters and then later re-replacing Talia with Lyta in the second season.
Breaking Bad: Christian "Combo" Ortega is one of Jesse's friends and the first fatality of Jesse and Walt's organization, killed by a rival gang. When Jesse reveals the news:
The Ninth Doctor, who was in only one series of 13 episodes. As he also has barely any Expanded Universe material, this makes him by far the shortest-lived and least-featured Doctor.
Until the War Doctor, who appeared in only 2 episodes and one mini-sode of the series before his regeneration.
The Eighth Doctor is an aversion. Although he has a reputation of being the shortest-lived Doctor due to only having two on-screen appearances (the 1996 movie and the 50th anniversary prequel mini-sode, The Night of The Doctor, in which he regenerates), he has actually appeared in more stories than any other Doctor thanks to his extensive appearances in audio plays, novels, and comics.
Katarina joins the TARDIS crew in "The Myth Makers", and dies early on in the serial immediately following it, "The Daleks' Master Plan". The same story also introduces a companion named Sara Kingdom, who is killed in the final part.
Quite a few of Sylar's victims, whose fascinating powers are quickly swallowed up into his repertoire, preventing most of them from seeing any interesting use. Perhaps most notable among these was Hiro's Love Interest Charlene "Charlie" Andrews, who is introduced and immediately killed. Hiro goes back in time to prevent her death… and fails, so (depending on how timeline shenanigans work) she was introduced and killed twice, in the span of two episodes. Later Hiro again tries to undo her death, and actually succeeds… and then she's immediately whisked away by ''another time traveller''. Hiro finally finds her… only to recognize that she, having been dropped off in the past and having lived another full life complete with grandchildren (all of which occurs off-screen), deserves to have her life left intact and decides not to try again.
This happens to an astonishing number of Primatech's female employees: Eden McCain, who has a short but memorable run as a plant monitoring Dr. Suresh before she tries to kill Sylar, who effortlessly No Sells and murders her; Candice Willmer, who has a similarly short yet memorable run as a Company agent tasked with capturing and keeping watch over Micah Sanders and later Sylar, up until he abruptly murders her; and lastly but most notably, Bridget Bailey, a psychometric women who may very well hold the world-record for this trope, as she has a single scene in which she's introduced to Sylar and then, say it with me, immediately murdered. In fact, she's brought in expressly for this purpose (Angela flatly states she called her down solely so Sylar could kill her), and doesn't even get a line — we only ever hear her scream.
There's also Nathan's supersoldier Scott in Season 3. He is introduced in the third season as the top Marine in the Pinehearst super soldier program. The episode climax is devoted to his injection with the ability-inducing formula, which grants him the power of super strength, and the episode ends with others questioning his status; he grins and says "I feel good". In the very next episode, he is promptly and unceremoniously murdered by minor villain Knox, who walks in and snaps his neck without any resistance.
House: Dr. Amber Volakis, otherwise known as "Cutthroat Bitch", is an example. First appeared in Season 4, Episode 2, died in Season 4, Episode 16 (the finale of that season). But a hallucination of her is vital to the plot of the following season's finale.
Las Vegas: In the two-part episode "Three Weddings and a Funeral," the writers poke fun at the inscrutability of Montecito owner A.J. Cooper by doing a couple of small reveals (and several implied off-screen reveals) about his past. He is then apparently killed off-screen in a plane crash, but shows up in the final minutes of the second part, crashing his own funeral.
Almost all of the Tail Section Survivors fall into this category - in particular, Libby had an often-hinted-at character that stood almost entirely unexplored when she was killed, seventeen episodes after her introduction. (her backstory continued to go unexplored until an episode late in the final season). Also, the infamous Nikki and Paulo.
In a repeat of the Tailies, out of the freighter crew only 2 characters (1 main and 1 recurring) remain alive just a season after their intro (keep in mind that both seasons were quite short compared to the first three).
Men Behaving Badly: Dermot was only there in the first series out of six. He was replaced by Tony, who most fans agree is a much better character, but still....
Merlin: Freya, who was introduced as a Love Interest to Merlin simply so that the writers could kill her off at the end of the episode, thereby making her a spirit that could retrieve Excalibur from the bottom of the lake.
NewsRadio: Invoked Trope in-universe, where some guy named Ted who none of the main cast knew about died in what seems to be a freak accident with a photocopier. It ultimately turns out that nobody knew anything about him, and the episode ends with Dave attempting to deliver a eulogy, citing the fact that "Ted" was a Star Wars fan, along with the newly-discovered facts that he was a member of the Klu Klux Klan (due to Klansmen comprising the entire audience) and enjoyed tennis.
Orphan Black: Has clones Katja and Beth, who don't survive the scenes that introduce them - though this is a Subverted Trope, since Sarah goes on to impersonate both of them and has a few scenes where her character is playing Beth in almost every episode of the first season.
Reality Show: A non-lethal example is on this type of show that feature all of the contestants in the opening credits, and then promptly kick off one contestant/team in the first episode.
Red Dwarf: Petersen, who we never see again after the Series 2 episode Statis Leak. The novels imply that his return in Series 8 would have made for some hilarious moments, if only the actor had been available.
Another example is Jonas Quinn. He was created out of whole cloth as a replacement for Daniel Jackson after Michael Shanks decided to leave, and stayed as a member of SG-1 throughout the sixth season. Then, after Shanks changed his mind, he was written out, came back in one episode of the seventh season, and after that, was never seen again.
Star Trek: The Next Generation also had Ensign Sonya Gomez, who appeared in two consecutive episodes in the second season, featured so prominently that viewers could only assume she would be a recurring character, then never was seen or mentioned again.
Similar high-profile guest stars that only appeared once or twice include Selar, Jellico, Shelby, and Robin Lefler...who would all feature prominently in the Star Trek: New Frontier novel series... and Jellico would eventually become fleet admiral in the Expanded Universe.
In Season Eight, we meet John's father, Henry Winchester, who is a member of the Men of Letters - a secret society dedicated to studying the supernatural. Of course he dies in the same episode he's introduced.
Averted by Samuel Campbell, Mary's father. Sure, he dies in "In the Beginning"in Season Four, but then he comes back as a secondary antagonist in Season Six.
Sookie's fairy godmother Claudine was hyped up to be a very mysterious, interesting character at the end of the third season, and also she appeared to be very important to the plot, especially in the season 4's first episode, where she lead Sookie into the fairy-realm and was revealed to be of ambiguous morality, participating in a human-harvesting plot and all.. And then, the next time she appears in season 4, it takes Eric about ten seconds to drain her dry and see her disintegrate into glittery dust. It gets even weirder when you realize that in the books the series is based on, she was a very central character and she didn't die till much later!
Partly a Justified Trope as her brother Claude is supposedly going to fulfill her role in future seasons of the show.
...Until he died too, and the show seems to have cut all the book's fae-related characters and plots with the sole exception of Sookie's powers.
Lexi, who was adorable, sweet, wise and... promptly staked. The only upside to this was that at least she never fell victim to the dreaded Forgotten Fallen Friend disease.
Mason Lockwood, who was killed off quite quickly after his introduction with just a five or six-episode stretch as the Always a Bigger Fish. All we really learned was that he was very protective of his family, he was sleeping with Katherine, and he had a bitchy werewolf friend who came back to haunt us. The writers like this one, because we also have: Jules, who was pretty much just a slightly sympathetic jerk who tortured Caroline, taught Tyler how to be a werewolf, was used by Klaus, and, oh, died. All after about four episodes.
Logan Fell. Not that we really wanted to get to know him....
Vicki Donovan, who is looking to be back for a while now that Jeremy and Matt are back from the dead, but it doesn't last.
Pearl, who seemed pretty cool, but ended up dead because of John. (Who, while showing up quite often, was also a bit of this trope.)
Zach too, who is apparently Stefan and Damon's nephew.
Mr Tanner, Harper....
Veronica Mars: Ms. Dent disappeared without explanation eight episodes into the first season due to budget constraints (and the fact that her character didn't really have much to do). Her exit is explained as maternity leave in a throwaway line a few episodes later.
The Walking Dead has many examples of this, but perhaps the biggest one is with the character T-Dog. He was Demoted to Extra the moment he first appeared, only getting screen time to be the Butt Monkey. This was especially the case in Season 2 where for majority of the episodes, he doesn't even get any lines of dialog. It got so bad, it was even lampshaded by T-Dog, himself, during an episode of Season 2 after he got a blood infection from a cut. And in the beginning episodes of Season 3, he is killed off after another black man is introduced, who dies even quicker than T-Dog, but had more lines of dialog and Character Development beforehand.
In Eternal Sonata, you only get Claves in your party for one short section of the game before she leaves, only to be mortally wounded soon afterwards. What's notable is that she then spends a good ten minutes lamenting her fate before she dies alone.
In Metroid: Other M, Samus meets up with Adam, Anthony, and four other federation soldiers on the Bottle Ship. Of the four soldiers, three are dead within the first third of the game, the body of one of which is never found, and the other dies later on. None are characterized very much. K.G (he who was never found) in particular gets just two lines.
Mhairi of Dragon Age: Origins – Awakening is introduced during the first area, given some hints of a personality, and even has an opportunity for you to gain or lose approval, before failing the Joining and dying.
Orsino is introduced in the end of the second act of Dragon Age II, has a few scenes in the third act before going One-Winged Angel and getting killed by Hawke in the finale no matter what decisions you made.
In Neo Contra, Mystery G. You fight him as the Mid Boss of Stage 2, and if you do well enough, he performs a Heroic Sacrifice in Stage 5 to save you from Master Contra. Last thing he does before dying is give Bill Rizer a Rousing Speech about how Bill isn't a fake if he risks his life fighting for his ideals.
In the second Wing Commander game, Elizabeth "Shadow" Norwood is Blair's only friend for the years after he was accused of allowing the Tiger's Claw to be destroyed. She serves as his wingman during the first set of missions, but then gets killed off, a victim of Retirony.
Can also be invoked to Blair himself during the funeral by dying right in the first mission of the first game.
Hinawa of MOTHER 3 is killed in the first chapter of the story, right after the player gets relatively attached to her.
Homestuck: The Black Queen in both iterations of the kid's session. In the Beta session, Jack killed her and took her Ring of Power after getting sick of being forced into clown outfits. In the Alpha session, she's killed offscreen by Betty Crocker.
There's also both Kings who barely get any screentime in all sessions before they're quickly offed.
Also, Tavrisprite, who existed for three panels before killing itself out of self-hatred.
Hegemonic Brute hardly gets any screen time in either human session before getting killed.
Poor HEGEMONIC BRUTE. His time in the spotlight has been cut tragically short. You almost feel sorry for the guy.
For the adventure game Kickstarter, a pledge of $10,000 would allow you to make a fantroll canon. However, the prize for an amount of $100,000 was 'your fantroll becomes canon and lives beyond one page.' Two people opted for the first option. Sure enough, the trolls lasted exactly one page before they were violently killed off.
Hetty from Gunnerkrigg Court. After Reynardine saw how horrible she was, he promptly killed her off within the very chapter her character was introduced.
Any number of fodder/fringe characters in Survival of the Fittest. In the abduction scene (the prologue of each game) teachers are almost invariably killed off, usually after being introduced only at the beginning of the scene. This also holds true for characters that die very early on. Britanny Ashworth of V2, as well as Tyson Neills and Anthony Burbank of V3 were all killed off in their first scene. (in the case of the latter pair, first post)
During his review of the movie Patch Adams, the Nostalgia Critic created an expy of the titular doctor (as portrayed by Robin Williams) called Dr. Bitch Spasms. The critic shoots him dead within moments. He does mention him in the next review, but only to confirm he's not coming back.
Nostalgia Critic: Oh he's still dead. I should do something about his corpse, he's starting to smell.
Exaggerated in Twitch Plays Pokémon with CCC the Hitmonlee. In a cooperative playthrough going continuously for over a week at that point, he only existed for about 38 minutes before being accidentally deleted.
In Noob's Season 3 Celebrity Star episode, the character played by the celebrity in question created an avatar, joined the main guild, obliviously used Real Money Trade and got banned from the game for doing so within about an hour.
Morph in the 1992 X-Men animated series. (Revived later in the series as a villain, but you can't blame this trope for people not staying dead. Especially members of the X-Men.)
In the comics, John Proudstar was introduced as a member of the All-New All-Different X-Men...and promptly killed off in the next storyline. And he stayed that way.
Galvatron: "SILENCE! There's much to do. We will attack other planets, we will suck them dry, we will rebuild a planet a hundred times more powerful than Cybertron! And I will RULE THE GALAXY!!"
Zarak, oh so calmly: "Who shall rule?"
Galvatron: "MEE! It is MY DESTINYYYYY!!"
Zarak, still oh so calmly: "We shall see, Galvatron. We shall see..."
There's also the Autobot Punch, the spy, who becomes the Decepticon Counterpunch. Sixshot has six modes. Mindwipe is a giant bat who can Mind Control anyone, and talks all spookily about the powers of darkness. The rest came and went too fast to really leave a mark, seeing how this three-parter introduced more characters than the entirety of season three.
Transformers Prime gives us Cliffjumper, who died in the pilot episode ten minutes in, came back as a zombie in the 2nd episode and then died again just as fast.
From Transformers Animated is Blurr He had a cameo in "Velocity", was formally introduced in the last episode of Season 2 and suffered a horrifying on-screen death in the first episode of Season 3.
Buckley from King of the Hill. We hardly knew anything about him before he was killed off, he appeared in at most about 10 episodes, he was kind of lazy and spoke in a monotonic voice, he loved to crack sex jokes, rarely showed any emotion beyond sarcasm, and we never knew his last name or met his family.
Total Drama Island: Ezekiel appears in the equivalent of four episodes of season one, barely spoke and after sending Women's Lib back about a century by being sexist to women, he was voted off first. In season two he appears more frequently, but only in the Aftermath episodes, and he talks even less. He comes back for season three, but is voted off first again - he appears in a few later episodes, but is no longer fully human for some reason, and ceases talking entirely. This is how he has been for the rest of the series up to this point. He was a very flat character; his main traits were being stubborn, having almost no social skills, and accidentally offending everyone, specifically women.
And as of season 4 Staci shared the same fate as Ezekiel did in season 1, due to her annoyance towards her team (Although Ezekiel was voted off in episode 2 of season 1, due to episode 1 ending on a Cliffhanger). The difference is that she got flung over.
And as of the premiere of Pahkitew Island in Italy, Beardo shared the same fate as the two, making this a borderline example of Black Dude Gets Eliminated First.
Several characters in Animals of Farthing Wood were only around for 1 season or a few episodes before they were killed off. A few such examples are the Pheasants, Dreamer, Bounder, the baby field mice, and the Newts.
Villainous example: King Sombra from My Little Pony: Friendship Is Magic: We don't get much introduction other than that he was an evil sorcerer king whose body was destroyed by Celestia and Luna, and during his two-parter "The Crystal Empire", he shows off very minimal characterization, then he dies at the hands of his former slaves the end. According to Meghan McCarthy, this was intentional.
Season 2 episode "Dragon Quest" introduced Peewee, a phoenix chick pet for Spike. The next time we see Peewee is in the Season 3 episode "Just for Sidekicks", in a series of photos showing Spike returned Peewee to the wild to be raised by adult phoenixes.