Second Episode Introduction

""Oh, please. If there were new guys, they'd have shown up in the season premiere.""

- Denny Crane, Boston Legal

The series Pilot has to do a lot of things. It has to establish the main character, set up the central conflict, and convince the network execs to okay the series. Usually, you can introduce all of the main characters in this process.

Occasionally, though, a secondary character can't quite get shoehorned into the introductory story and just don't exist in the pilot. Alternately, sometimes the networks execs approve the show, but decide that it needs a few extra characters, so the creators introduce these characters in the next episode. Sometimes, cast members show up for a Pilot Movie but don't agree to come back for the series.

Any of these qualify as the Second Episode Introduction. The key characteristic is that whoever is being introduced must show no signs of existence in the pilot, and must be a regular cast member from that point onwards.

Anime and Manga

 * The first episode of Pokémon had The Hero and his trainer, The Rival, the Mom and The Professor. In that episode, said hero encountered a vengeful being who's quite overprotective over what it considers its territory. Oh, and that Fearow was quite rough as well. But the episode didn't have an iconic feature of the series that would become (to some) trite over time. (And by "time" I mean the course of a decade.) Oh, and Team Rocket wasn't in that episode either.
 * In Hamtaro, Dexter, Howdy, Pashmina and Penelope are introduced in the second episode, while Cappy, Panda, Maxwell and Sandy show up in the third.
 * In Le Chevalier d'Eon, two of the five main characters don't appear until the second episode.

Live Action TV

 * Babylon 5: Several of the cast regulars, like Dr. Franklin, Ivanova, and Talia were not present in the Pilot Movie.
 * In fact, Dr Franklin didn't show up for the first proper episode either -- he actually was a literal Second Episode Introduction.
 * Lennier wasn't introduced until the fifth episode. Na'Toth was also introduced in the fifth episode, although she was a replacement for the character Ko'Dath who had been introduced in the third episode (the actress who played Ko'Dath quit after one episode due to troubles with the prosthetics, so Ko'Dath fell victim to an offscreen airlock accident).
 * In the Scifi series The Invisible Man, the Keeper shows up in the second episode. This seems to be the second type, because it would have been easy to work her character into the pilot.
 * The two JAG episodes that act as the pilot for NCIS had a character named Vivian Blackadder on Gibbs' team. She was dropped for the series proper, so the first real episode introduced Caitlin Todd as a secret service agent who transferred to NCIS for episode 2.
 * It happened again for NCIS Los Angeles - Special Agent Macey was introduced as the head of the LA branch in the two-parter pilot on NCIS. Come the series proper, Macey's been replaced by Hetty.
 * Matt Parkman in Heroes, who in a variation was originally intended to be in the pilot, but whose introduction was delayed until the second episode instead.
 * Dr. Leonard "Bones" McCoy didn't appear in either of the two original pilot episodes of Star Trek the Original Series, though this is an unusual case in that Gene Roddenberry very much wanted DeForest Kelley to play the doctor, but he yielded to the casting choices of each pilot's director (John Hoyt as Dr. Philip Boyce, and then Paul Fix as Dr. Mark Piper). Kelley finally appeared in the first regular episode to be produced, "The Corbomite Maneuver". Of course, since the episodes were aired out of production order, McCoy appeared from the start anyway.
 * Yeoman Rand was the third (and last) attempt at following Roddenberry's directive of a sexy female Yeoman who has UST with the Captain, and also made her debut in "The Corbomite Maneuver".
 * Uhura also debuted in "The Corbomite Maneuver"; in fact, Nichelle Nichols shares both her first and last Star Trek appearances with DeForest Kelley.
 * Scotty and Sulu are partial examples, in that they did both appear in the second pilot, though basically as glorified extras whose roles were substantially changed and assumed their proper form in "The Corbomite Maneuver". (In the second pilot, Sulu, the ship's helmsman, was instead the chief physicist.)
 * JJ of Criminal Minds, who is later shown to be an integral part of the team, isn't present or even mentioned in the first episode.
 * Elaine Benes did not appear in the Seinfeld pilot because the character had not yet been created. She was added to the second episode when NBC demanded that a woman be added to the show or they'd cancel it.
 * Firefly (yes, another Firefly example) has an interesting spin on this that the second episode reintroduces all nine characters. After the pilot had been shot and screened for FOX, they said they wouldn't show it first so the writers had to rewrite the second story to reintroduce everyone. Then when there were doubts that that would be used first by FOX, they rewrote one in the middle of the series to reintroduce everyone. And then when they got round to the the movie, they had to introduce the characters for a FOURTH time for everyone who hadn't seen the show.
 * Godber and all other prisoners except Fletcher himself do not appear in the pilot of Porridge.
 * Juliet O'Hara was introduced in the second episode of Psych.
 * Sara Sidle, despite being one of the most popular CSI characters, doesn't appear until episode 2.
 * Dylan McKay is conspicuous by his absence in the pilot for Beverly Hills, 90210 (yes, the title had a comma in the pilot's opening credits), showing up from episode 2.
 * Claudia doesn't show up in person until the fourth episode of Warehouse 13.
 * In Eureka, Nathan Stark arrives at the beginning of the second episode. The pilot instead has a different obnoxious Nobel laureate who is Fargo's boss, has sexual tension with Allison, and seems to be developing a mutually antagonistic relationship with Carter.
 * Clyde Langer did not appear until the second episode of The Sarah Jane Adventures, replacing Kelsey in an inversion of Affirmative Action Girl.
 * Charlie wasn't introduced on The West Wing until the third episode, but he was made a series regular immediately and held the honor for the rest of the run.
 * Betty Draper appears for maybe two minutes in the pilot of Mad Men--series creator Matt Weiner actually had to write extra scenes for the audition process, which were later incorporated into an episode. Naturally, Betty became a major character from the second episode onward.
 * When Coach's actor ended up having to leave New Girl due to an unexpected pickup of a second series of an existing show (Happy Endings), his role was replaced by a Suspiciously Similar Substitute for the second episode.
 * Eli Stone didn't introduce Maggie, a main love interest and Eli's partner, until the second episode.
 * Brooke Davis on One Tree Hill, who quickly became an Ensemble Darkhorse and one of the show's leads.
 * On Community, Señor Chang does not appear until the second episode.
 * Rather than a character, Power Rangers often holds off on debuting either the Megazord or even the Transformation Sequence until the second episode of a two-part premiere. Sometimes they do both in a two-stage version: air both parts of the premiere on the same day with the first transformation happening in the second half, then bring out the mecha in next week's episode.
 * The first season of Mighty Morphin Power Rangers averted this in its adaptation of Kyoryu Sentai Zyuranger: in the original series it took several episodes for Daizyuzin (the Megazord) to be introduced, but it was an integral part of the Rangers' arsenal in MMPR, so a later mecha fight was moved up to the first episode.
 * In Power Rangers Lightspeed Rescue, we don't meet monster-maker Jinxer until episode two (which is interesting - he wasn't there when the villains were unsealed, so was he on Earth all along?)
 * On Drop the Dead Donkey, Sally Smedley first appears in the second episode. Justified as a personnel decision by the new CEO.
 * Doctor Who introduced iconic supervillains the Daleks in the second story. However, this is an inverted trope, as this was much earlier than the staff had originally intended to introduce the alien villains.
 * District Attorney Adam Schiff (Steven Hill) of Law and Order is notable in that he appeared in EVERY EPISODE of the first 10 seasons EXCEPT for the first one, which was produced before Hill had joined the cast.

Radio

 * Zaphod Beeblebrox, Trillian and Marvin the Paranoid Android were all introduced in the second episode of The Hitchhikers Guide to The Galaxy.

Web Original

 * Lifepoint One Entertainment introduces the title character of Xin at the end of the third episode after setting the stage and setting up the conflict between Andre and Ghai, the two major bad guys of the series.
 * The only main characters in the Homestar Runner universe who appeared in the original story "The Homestar Runner Enters the Strongest Man in the World Contest" were Homestar Runner, Strong Bad, Pom Pom, and The Cheat. Bubs and Coach Z were introduced in the second story, "Where My Hat Is At?", and other characters came later.

Western Animation

 * Futurama introduces the supporting Planet Express crew -- Hermes, Amy and Zoidberg -- in the second episode.
 * "What about that guy?"
 * "He's Scruffy. The Janitor. He came along later. He's on break."
 * Commander Zhao, one of the main antagonists of the first season of Avatar: The Last Airbender. In the same episode we are introduced to Zhao, we are first shown the ruins of the genocide of the Air Nomads.
 * Gus and Miss Grotke are introduced in Recess not in the second episode, but part B of the first episode. For the former, it was his Welcome Episode. For the latter, it was more "She wasn't in the first part, so here she is".