Not Named in Opening Credits

If you want to surprise the audience, you don't put the name of the actor for the surprise character in the opening credits.

Contrast Spoiler Opening when something in the opening of the show ruins a surprise.

See also Sir Not-Appearing-In-This-Trailer and Character as Himself.

Anime and Manga

 * GA Geijutsuka Art Design Class is a rare anime example. A character was introduced in episode 6, but he was given an one-line speaking role in episode 5. In that episode, he was only listed as "Grade 11 Student -- M.S."
 * In the anime series Baccano, is left nameless in the opening sequence. Oh, and, which means he's totally insignificant and unimportant, right? WRONG. As it turns out,

Films -- Live-Action

 * John Doe in Se7en. insisted on this to avoid spoiling the killer's identity. The producers had wanted to give him top billing, so as a compromise, his name is the first thing shown in the closing credits.
 * Star Trek III the Search For Spock did not list Leonard Nimoy as an actor in the opening credits, though it did mention him as the director. What they did do in the opening credits was, since Nimoy's name had always directly followed Shatner's, simply leave a gap for several seconds where Leonard Nimoy would have been listed, showing no name at all before moving on to DeForest Kelley and the other cast members.
 * In the movie Tropic Thunder, the heavily-made-up isn't mentioned anywhere until the final credits roll. Neither is.
 * The 1931 film version of Frankenstein famously omitted Boris Karloff's name in the opening credits. Instead, the Monster is billed with a question mark.
 * In turn, the 1935 Bride of Frankenstein bills "The Monster's Mate" with a question mark, and only gives Elsa Lanchester credit for playing Mary Shelley in the prologue.
 * From Russia with Love takes the cake on this one. Blofeld's debut as the Big Bad of the James Bond movies starts the tradition of keeping his face off-camera, prompting the use of this trick to make sure nobody could be sure what he looked like. Furthermore, not only is there no hint as to who plays him in the opening credits, the character is never referred to by name (he is addressed as "Number One" exactly once) in the movie itself. Finally, the ending credits acknowledge his existence by crediting one Ernst Blofeld with a question mark in place of the actor, prompting the audience to keep coming back.
 * Jack Nicholson in Broadcast News.
 * Sleuth was probably the only example in cinema history to do the exact opposite of this and pad out the opening credits with false names. The remake did not bother with this move, in what has to be the dumbest revealing of a spoiler ever.
 * Gary Oldman in Hannibal. He chose not to be credited after his request for above-title billing was rejected (since Anthony Hopkins and Julianne Moore already had it and MGM didn't want too many names above the title) but he was billed third in the closing credits for the video release.

Live-Action TV

 * Twenty Four has done this three times, twice for recurring villains.
 * The X-Files often did this, at least twice with Nicholas Lea (Alex Krycek), who often popped up at surprising points late in episodes, and one notable time with the not-quite dead Cigarette-Smoking Man (William Davis).
 * The seventh season Premiere of Buffy the Vampire Slayer did this with the surprise cameos of the former Big Bads at the end (actually the First Evil). Additionally, Buffy subverted this by adding the name of a character that would be killed off in the same episode to the opening credits for a single episode.
 * The unexpected reappearance of in the penultimate episode of season six was kept from the opening credits, and even  was changed, giving the impression the character was gone for good.
 * Angel took a different approach: the character in question had made several appearances in flashbacks but hadn't appeared in "the present" for over two seasons. Thus, viewers were associating her name in the opening credits with "there will be a flashback in this episode" instead of "she will appear in the final minute of the episode to shock us all."
 * Angel also played it straight on at least four occasions - Darla at the end of Season 1, Faith in the opening episode of season 2, Drusilla in Season 2 and Lindsey in Season 5.
 * Doctor Who frequently used pseudonyms to disguise appearances of The Master, or (in at least one instance) Davros.
 * Averted in spectacular fashion for "Journey's End" twice! The Radio Times (The BBC's own Listings Magazine!) published a cast list with David Tennant playing the lead for the episode, four days before the episode was set to broadcast. This could have been easily handwaved by saying that the regeneration cliffhanger of the previous week's episode was so secret the Radio Times didn't know until it was broadcast and then there was no time to alter the listing before publication. Yet the listing acknowledges the regeneration and still prints Tennant's name under the lead role. Then when the episode airs they recap the last episode, complete with cliffhanger, then show the title sequence, still with Tennant's name in it, then resolve the cliffhanger.
 * Patrick Troughton & Tom Baker do not get credited for their post-regeneration appearances in their predecessors' final episode.
 * Tom Baker doesn't get credited for his (archived) pre-regeneration appearance in his successor's first episode.
 * Famously averted to the point of inversion. William Hartnell's contract stipulated that he would be credited in every episode yet no mention was made of him having to appear in every episode. So, in "Mission to the Unknown", when all the regular actors had the week off and the episode was entirely populated by guest roles played by guest actors, Hartnell got the lead credit despite having no screen time in the episode. The actors playing the companions had no such stipulations in their contracts.
 * Billie Piper's return in the fourth series through a series of tantalizing semi-appearances (fizzing into the air, breaking through a televised transmission, always unseen) was kept under painstaking lock and key by the BBC: the screening of the first episode "Partners in Crime" cut out her scene until the air date, and didn't include her name in the credits at all. The last five minutes subsequently set whogasms squeeing and conspiracies rearing.
 * J. Michael Straczynski had intended to do this in a third season episode of Babylon 5 wherein Capt. Sheridan's Only Mostly Dead wife (played by Melissa Gilbert, wife of Bruce Boxleitner who played Sheridan) reappears on the station in the final seconds of an episode. Gilbert's contract, however, required him to list her as a guest star. However, the credit referred to the character in question without her family name, so the wham effect was maintained for those who didn't make the logical leap.
 * Again, Straczynski wasn't able to do this for the episode in which Na'Toth turned out to be Not Quite Dead - and in this case, the character only had one name, so the credit had to read "Julie Caitlin Brown as Na'Toth", spoiling the surprise.
 * He did manage to do this with in Day of the Dead.
 * In "Crossroads, Part 2", the season three finale of Battlestar Galactica,.
 * They did it again in "Sometimes a Great Notion", to hide The Reveal that.
 * Stargate Atlantis.
 * Much earlier, its parent show omitted Peter Williams' name in the opening credits of the episode where Apophis comes Back From the Dead in the last few minutes.
 * Stargate Atlantis did it again during "The Kindred, Part I". When, the guest credit for   was placed in the ending credits to maintain the surprise.
 * Except that in some teaser trailers, the end of the episode was shown, so you are just wondering when it will take place.
 * An episode of Supernatural (I think it was the second season finale, but I'm not sure) did this with John Winchester. The name of the actor who played him was the very first credit at the end.
 * Supernatural did this again in season six: in the episode where it is revealed that,   is not credited in the opening sequence.
 * A much more recent episode featured the return of . was left uncredited in the episode to keep the big return a surprise.
 * Twin Peaks did this for the return of Andrew Packard.
 * Inverted with the House episodes after his team had quit in the season 3 finale, but were still prominently featured in the opening credits in season 4. Guess what? They were back within three episodes.
 * But played straight by House when late in season 4.
 * And when in the last few episodes of Season 5.
 * This was broadly inverted in the first few episodes of the final series of Monty Python's Flying Circus. John Cleese had decided against continuing with the television version of the show, and did not appear, but was nonetheless credited for some sketches that had been reworked from earlier Python projects. Of note, the second episode was based on an early draft of Monty Python and The Holy Grail.
 * Busy Philips was always listed as "Also Starring Busy Philips as Kim Kelly" on Freaks and Geeks, despite the fact that Seth Rogen was billed on the opening credits and didn't always appear.
 * Also the fourth episode was named "Kim Kelly is my Friend", not bad going for a last minute addition.
 * They did this with Fionnula Flanagan in Lost.
 * Francois Chau is always uncredited for playing Pierre Chang, even after.
 * Greg Grunberg was not named at all for his cameo in the pilot.
 * Variation: Press releases for the season 3 finale and various season 4 episodes intentionally left out Malcolm David Kelly and John Terry so as to not spoil their sudden, brief reappearances. They were credited on the episodes proper, however.
 * Hugely inverted for the finale, where every single former cast member and recurring guest character who appeared in the episode were credited in the same sequence as the main cast, leading to a whopping 28 actors credited as 'starring'.
 * They inverted the trope in their handling of Harold Perrineau in season 4, crediting him for every episode even though he didn't appear straight away. The fact that Michael would reappear and his reason for doing so were revealed shortly before he was first seen onscreen, but his name in the credits before that gave it away.
 * Inverted in the closing credits of Part 1 of of the two-part Are You Afraid of the Dark? episode "The Tale of Cutter's Treasure". One mysterious in-story character's face was never shown to add suspense, but his name is revealed in the cast credits. This wouldn't be a problem if the character wasn't one of the two reoccurring ones. Fans of the show would likely recognize his voice, but it ruined the reveal in Part 2 for anyone who watched the credits.
 * The Star Trek: Deep Space Nine episode "Heart of Stone" did this for, since was  until very near the end.
 * Not necessarily a case of a surprise character but a series regular: William Devane was left out of the credits of the short-lived 1993-94 ABC sitcom Phenom at his request, after he campaigned to get starring credit in response to his Star-Making Role in Knots Landing (trying to get either top billing or second billing in the cast, between co-stars Judith Light and Angela Goethals) but was rebuffed by show producers and ABC, because they felt that emphasizing Light as its star (although both Light and Geothals' characters were the primary focus of the show) and giving her top billing would draw in female viewers and fans of Light's previous series, Whos the Boss; Devane eventually told the producers that if he didn't get a billing change, he'd rather not be credited for being on the show at all.

Theatre

 * In the play The Woman in Black, the actress who plays the titular character isn't credited in the program, which makes it out to be a two-man show. Therefore when a third actor comes on as the ghost...

Videogames

 * In Metal Gear Solid 4,
 * Somewhat subverted in that
 * Mitsumete Knight has two openings, the first showing the main heroines, the second the enemy Generals : only the first has the seiyuu (voice actors) written under each character. The probable reason behind this is.

Western Animation

 * Paul Lynde voiced the Hooded Claw (aka Sylvester Sneekly) in The Perils of Penelope Pitstop but he is not credited in this show, nor is he credited in the other show in which he furnished a voice that year, The Cattanooga Cats (as Mildew Wolf in the "It's The Wolf!" segment).