Mysterious Middle Initial

"Spaulding: My name's Spaulding, Captain Spaulding.

Chandler: And I am Roscoe W. Chandler.

Spaulding: I am Jeffrey T. Spaulding. I'll bet you don't know what the T. stands for.

Chandler: Uh...Thomas?

Spaulding: Edgar. You were close, though. You were close, though, and you still are, I'll bet."

- Animal Crackers

Many fictional characters' names are shown as a first name, last name, and a middle initial in between. If this initial is short for a longer name, it's never stated in Canon. A Mysterious Middle Initial could also be the entire middle name, or a joke about the character's lack of an actual middle name, or an attempt to conceal an Embarrassing Middle Name.

This is most likely because, it's easier to remember a middle initial (e.g.: "Robert J. Smith") rather than a full middle name (e.g.: "Robert James Smith") regardless of whether or not said middle initial actually stands for anything. It's going to become especially egregious in anime when a character with a very Japanese name has an English middle initial. See also Embarrassing Middle Name.

Anime and Manga

 * One Piece: Many of the world's most powerful people have the middle initial of "D", and nobody seems to know what it means or what it stands for, aside from signifying you're a badass. This has been referred to as the "Will of D," and it is even recognized by characters in the story.
 * Yu-Gi-Oh! has Pegasus J. Crawford-- the J. was chosen deliberately as a tribute to all those cartoon characters with J for a middle initial.
 * The Anthropomorphic Personification of America, Alfred F. Jones, in Axis Powers Hetalia. Fanon says that the "F" stands for "Fuck Yeah!" In one of the blog posts, Himaruya said that the F stands for either 'Foster' or 'Franklin'. But the fandom generally ignores this.
 * Solf J. Kimblee, everyone's favorite Mad Bomber from Fullmetal Alchemist.
 * Gilbert G.P. Guilford of Code Geass has two mysterious initials.
 * Nicholas D. Wolfwood of Trigun, although when asked, the creator has offered a variety of (funny) possibilities.
 * Touma H. Norstein of Digimon Savers.
 * Elmer C. Albatross from Baccano!
 * Although it's not his real name, Setsuna F. Seiei of Mobile Suit Gundam 00
 * According to Word of God, his Code Name is very prophetic.
 * The Mr. Alt Disney Will B. Good in Ergo Proxy- also a Punny Name.
 * In the English dub of Tokyo Mew Mew, Akasaka Keiichiro's name was changed to Wesley J. Coolridge III. It's doubtful even 4Kids knew what the "J" stood for.
 * Likewise, 4Kids's dub of Ojamajo Doremi changed Senoo Aiko's name to Mirabelle P. Haywood. Again, no idea what the "P" meant.
 * Though it's just a regular Mysterious Initial, Count D of Pet Shop of Horrors is always known simply as Count D. The chapter titles, however, are all words that begin with the letter D. Suggestions, perhaps?
 * Takamichi T. Takahata (seriously, what is a thoroughly Japanese name like that doing with a middle initial?) and Takane D. Goodman of Mahou Sensei Negima.
 * Another example of a Mysterious Middle Inital in a very Japanese name-Kotetsu T. Kaburagi of Tiger and Bunny.
 * Last Exile has Alvis E. Hamilton.

Comic Books

 * Scott Pilgrim features both Scott W. Pilgrim and Ramona V. Flowers. While we learn that the "V" in Ramona's name stands for "Victoria", we never learn what "W" stands for in Scott's name.
 * A Felix the Cat comic story had Felix operating as a private detective under the name of Felix T. Cat. When asked, he says that the "T" stands for "The".

Film

 * Many of the characters played by Groucho Marx: Captain Jeffrey T. Spaulding in Animal Crackers, Rufus T. Firefly in Duck Soup, Otis B. Driftwood in A Night at the Opera, Hugo Z. Hackenbush in A Day at the Races.
 * Harris K. Telemacher in L.A. Story.
 * Dr. Frank N. Furter. Sure, his full name is a play on both "Frankenstein" and "Frankfurter (hence the infamous "You're a hot dog" line in the film). But, as the song Planet Schmanet/Wise Up, Janet Weiss indicates, Frank is his first name, Furter is his last name...and it's never revealed what his middle initial "N" stands for.

Literature

 * The Discworld book Maskerade has Perdita X. Dream, whose "X" stands for "someone who has a cool and exciting middle name."
 * In Thud! we even get introduced to deputy constable A.E. Pessimal, who - strictly speaking - does not exactly fit this trope, since he wasn't named as a child, he was "initialled", so A.E. is his full first (or first and middle) name.
 * Dr. John H. Watson
 * You can make a pretty good case for the 'H' standing for either 'Hamish' or 'Henry.' In 'The Man with the Twisted Lip' Mrs. Watson calls the good doctor 'James,' and it is proposed that is a pet nickname/pun derived from his middle name (Hamish is the Scottish variant of 'James') Otherwise, this would mean that Mrs. Watson forgot her husband's name, which would be a bad thing. Alternatively, he could be named after Cardinal John Henry Newman, who was an influential figure around the time Watson would have been born, and a lot of people were named after him.
 * Moreover, Henry is a fairly safe bet because it was probably the most common male name beginning with H at the time.
 * It's just as likely his creator forgot. Arthur Conan Doyle was notorious for changing names in the books, which is why Holmes's landlady is sometimes Mrs Hudson... and sometimes not. So if the H ever stood for something, there's no guarantee it was just one name.
 * All of the characters in the book The Circus of Doctor Lao have the middle initial R.
 * Harriet M. Welsch doesn't really have a middle name. She added the initial herself.
 * Although in Harriet Spies Again she claims the M stands for Middle.
 * The mentally-disabled titular character of So B. It calls herself "So be it", and her neighbor decided it was her full name, complete with middle initial.
 * In Michael Chabon's Summerland, Jennifer T. Rideout claims that the "T" doesn't stand for anything. We later learn that her middle name is Theodora.
 * W.E.B Du Havel from the Honorverse has three of them. They don't actually stand for anything.
 * Smug Snake Bob Ewell from To Kill a Mockingbird is named after the famous Southern general Robert E. Lee. whilst Lee's middle name was Edward, Ewell's full name is actually "Robert E. Lee Ewell".

Live Action TV

 * James T. Kirk's middle name, Tiberius, wasn't revealed in the original series. It was first mentioned in the semi-canon animated series, but it was confirmed in Star Trek VI.
 * William T. Riker on Star Trek: The Next Generation was thought to be a shout-out to James Tiberius Kirk, but was revealed in a later season to just be "Thomas".
 * Prior to this, in a (non-canon) novel Peter David had given it as 'Thelonius', probably in a homage to Kirk's style of middle name. He attempted to Retcon this with 'Thomas' in a later novel.
 * Or a homage to jazz musician Thelonious Monk and a reference to Riker's trombone playing.
 * In Family Ties, Alex P. Keaton got his middle name from an ad lib done by an actor who also fits the trope: Michael J. Fox! It was never revealed what the P. stood for, although given his parents' status as former '60s hippies, it's been suggested that it stands for "Peace".
 * Pendleton University's badger mascot is named Pendleton J. Badger.
 * "This is Stanley H. Tweedle, Captain of the Lexx..."
 * Fred Sanford of Sanford and Son had the middle intial G. but constantly changed what it meant for comedic purposes of what fit the scenario.
 * An episode of M*A*S*H sees Hawkeye losing it trying to find out B.J. Hunnicutt's full name.
 * Don't forget Maxwell Q. Klinger and Sherman T. Potter.
 * In the old 50's sitcom "The Many Loves of Dobie Gillis", Bob Denver played a strange beatnik character named Maynard G. Krebs. In one episode he admitted that the G. stood for "Walter".

Theatre

 * John P. Wintergreen in Of Thee I Sing. Ira Gershwin wrote that when he asked co-author George S. Kaufman what the initial stood for, he was told, "'Why, Peppermint, of course!' with a look that could only mean that any child knew that." (Kaufman's writing credits also include The Cocoanuts, Animal Crackers and A Night at the Opera, and his own middle initial is fairly mysterious.)

Video Games

 * Kenneth J. Sullivan and Ozwell E. Spencer from the Resident Evil series. Subverted with Leon S. Kennedy, whose middle initial stands for "Scott".
 * Rolento F. Schugerg from Final Fight and Street Fighter, whose full name is already obscure as it is, being mentioned only in a character profile for Street Fighter Alpha 2.
 * There's also William F. Guile from the Street Fighter film, which is not really the character's full name in the original games, but still counts as an example.
 * The Castlevania series has Trevor C. Belmont (Ralph C. Belmondo in the Japanese versions). Alucard subverts this though, whose real name is displayed as Adrian F. Tepes in the end credits of Dracula's Curse, has his middle name (Farenheights) mentioned in the Japanese version's manual and in the actual game in Castlevania: Symphony of the Night.
 * Farenheights is actually his mothers last/maiden name.
 * Klarth F. Lester from Tales of Phantasia and Fulein K. Lester from a spin-off sequel, Summoner's Lineage, despite the fact that no one else in their world in any time period has a middle initial.
 * Gaia Online's iconic eccentric businessman, Johnny K. Gambino. According to Word of God, "the world is not ready to know" what the K stands for.

Western Animation

 * Many cartoon characters have the middle initial "J":
 * "I am Ewmer J. Fudd, miwwionaiwe. I own a mansion and a yacht."
 * Also Wile E. Coyote, Super Genius?
 * The frog in "One Froggy Evening" was retroactively named "Michigan Frog" and given "J." as a middle initial because of this rule.
 * Rocket J. Squirrel and Bullwinkle J. Moose. The J was a reference to their creator, Jay Ward.
 * Parodied in a skit where Bullwinkle signs something with an X, Rocket queeries him for why he does so to which Bullwinkle replies "Its my middle initial"
 * Homer J. Simpson is a relatively well-known example. His middle initial stands for "Jay".
 * And his son Bartholomew J. Simpson. His middle initial stands for "Jojo".
 * And his father Abraham J. Simpson. His middle initial stands for "Jebediah".
 * Futurama never revealed Philip J. Fry's full middle name.
 * In SpongeBob SquarePants, there's Sheldon J. Plankton and Eugene H. Krabs whose middle initials stand for James and Harold respectively.
 * Recess has Theodore J. "TJ" Detweiler. In one episode Randall and Menlo try to blackmail him by threatening to reveal what the J stands for.
 * In the special All Growed Down it was revealed the J stands for Jasper.
 * Beezy J. Heinous on Jimmy Two-Shoes. Eventually revealed to stand for "Jo-Jo".
 * Stimpson J. Cat from The Ren and Stimpy Show.
 * Timothy Q. Mouse from Disney's Dumbo.
 * Bonkers D. Bobcat, whose mysterious middle initial is also a play on the word "the".
 * Thaddeus S. Venture.
 * Hey Arnold! has Helga G. Pataki, who promises a visit from Old Betsy for those who inquire too closely about the "G." Word of God says it's
 * Archimedes Q. Porter from Disney's Tarzan.
 * The Simpsons also have a mysterious first initial. In the "Who Shot Mr. Burns?" two-parter, it is revealed that Skinner's full name is "W. Seymour Skinner", just for the sake of adding him to the list of suspects that have for initials either WS or SM. This is never mentioned again in the series.
 * In one episode of the Pac-Man cartoon, Clyde gives his full name as Clyde Q. Ghostmonster.
 * Blooregard Q. Kazoo. Granted, he's an imaginary friend, and their names tend towards the silly and random, so he might not have a middle name at all.
 * The animated series based on The Berenstain Bears books gave Papa Bear a middle initial of Q.

Other

 * Alfred E. Neuman, the mascot of Mad Magazine.
 * John Q. Public, though the initial is often interpreted as "Quincy."
 * And, for a Mysterious First Initial, J. Random Hacker.
 * Red vs. Blue has Leonard L. Church and Michael J. Caboose, although even their first names are rarely mentioned, and Church's middle initial only shows up in a character profile on the DVD.

Real Life

 * Jesus H. Christ is a false example: the "H" is derived from "IHC", which was commonly mistaken to be a set of initials but is actually "Jesus" abbreviated in Greek letters (the H is an eta, and the C is a simplified sigma). For that matter, Christ is a title, not a last name, and only became permanently attached to his name after his death. Jesus was referred to instead as "Jesus of Nazareth" or "Jesus the Nazarean", or "Jesus the carpenter's son", or "Jesus, Mary's son." His parents were not Mary and Joseph Christ.
 * In Lamb, Christopher Moore jokingly proposes  as a possible middle name. "It's a family name. You know,  ..."
 * Hiram Ulysses Grant had a clerical error for a middle initial. At some point in the application process for West Point, his first name was dropped, and his middle name sprouted another S, which people assumed stood for his mother's maiden name, Simpson. Ulysses S Grant later decided that he preferred this name over General HUG, although he never officially claimed that the S stood for anything.
 * Another explanation floats around that rather than a mistake, he deliberately fudged his name on the papers because Ulysses sounded much cooler to him than Hiram, and U.S. Grant was pretty slick too.
 * Hollywood producer David O. Selznick's middle initial stood for "nothing" (i.e., 0).
 * Which becomes an injoke in Alfred Hitchcock's North by Northwest; protagonist Roger O. Thornhill similarly added his own middle initial -- and notes that his initials as a whole, as printed on his personalized matchboxes, are quite appropriate for an advertising executive like himself.
 * Harry S Truman's middle initial is usually written without the period, because "S" was his entire middle name. Both his grandfathers' names started with S and his parents didn't want to choose one over the other.
 * David X. Cohen, producer of Futurama. The X literally doesn't stand for anything. His real middle initial is S, but WGA and DGA rules required him to differentiate himself from another David S. Cohen -- he decided to go with something 'sci-fi-ish'.
 * Russell T. Davies also added a meaningless middle initial to his name to distinguish him from another Russell Davies.
 * Chiaki J. Konaka, creator and executive producer of Serial Experiments Lain, Digimon Tamers, and Texhnolyze (among other anime series), inserts a J into his name whenever it's romanized, despite the fact that Japanese names don't have middle names. Just like the above cases, the J is meaningless.
 * Michael J. Fox. The J stands for Andrew. Also for not making him "Michael, a fox" or "Michael, Eh, Fox?".
 * There was already an actor named Michael Fox, and SAG rules require that all active members have unique stage names.
 * He wanted to homage Michael J. Pollard (whose J stands for nothing) using that letter.
 * Barack H. Obama, while everyone knows what the h stands for, the official White House website breaks format (compared to the other bios) and does not mention it.
 * Newshounds creator Thomas K. Dye, who even signs his panels as "TKDye".
 * Iain Banks writes his science fiction novels, including The Culture series under the name "Iain M. Banks". The M is taken in part from Menzies being a family name, but like many other real-life examples, it's essentially a made-up middle initial.
 * J. K. Rowling used initials to disguise the fact she is a woman, in order to be taken more seriously. The K doesn't stand for anything -- legally, anyway. It was suggested by her publisher, as a way to get more boys to read her book. It comes from her grandmother's name Kathleen.
 * Legendary musician Booker T. Jones, of Booker T and the MGs. He was named for Booker T. Washington, but in Jones' case (unlike Washington's) the T doesn't stand for anything.
 * The journalist Jennifer 8. Lee. According to The Other Wiki, "Lee was not given a middle name at birth and chose her own middle name later. She chose "8" as a teenager because of the prevalence of her first and last names"
 * Vanessa L. Williams (the L stands for Lynn) was once known just as Vanessa Williams until someone else registered the name with the SAG before she could... so she wound up being known with the initial as well.
 * John C. Reilly, once again due to SAG regulations. (It stands for Christopher.)
 * Weezy F. Baby and the F is for....all these things.
 * The creator of Regular Show has two mysterious initials - J. G. Quintel. Fans have not yet managed to find out what either of them stand for.
 * An almost painfully frequent practice when referring to the General Authorities of the Church of Jesus Christ of Latter-Day Saints is to give one initial, one name, and the surname.
 * This is due to the large families Mormons typically have. The abundance of people who share similar names requires clarification. For example, three past presidents of the church were named Joseph Smith, Joseph F. Smith, and Joseph Fielding Smith.
 * Watergate figure Jeb Stuart Magruder, apparently named for American Civil War general James Ewell Brown "Jeb" Stuart.
 * Robert Q Lewis
 * W.C. Fields
 * It was once said about British politician H.H. Asquith that despite his position as Prime Minister everyone knew his name but not what the Hs stood for. (They stand for Herbert and Henry respectively.)
 * Johnny Cash was christened John R. Cash, where the R didn't stand for anything. His parents simply could not settle on a full middle name. Abbreviating this further, Cash was universally known as J.R. from infancy until he enlisted in the Air Force and wasn't permitted to use an initial as his first name, and so had to revert to his legal name of John.