Letter Motif

""Strange! I just realized that Lex Luthor has the same initials as Lana Lang! LL! -- Will Luthor become a great scientist? Or... a criminal?""

- Superboy in one of the many Lampshade Hangings on this trope in the Superman mythos

A way to connect characters, places, or ideas in a work of fiction is to give them a letter or syllable that ties them together. It might be ascribed to a family name or surname, but generally serves as a more general and subtle form of Theme Naming and Theme Initials.

Compare Alphabetical Theme Naming and Alliterative Name.

Anime and Manga

 * The Espada all have two of the same letters in their names (i.e. Starrk; Nelliel; Nnoitra; Yammy; Baraggan).
 * A couple of the Numeros and the Fraccion share the same double-letter motif (i.e. Aisslinger Wernarr; Charlotte Chuuhlhourne; Abirama Redder).
 * Most, if not all of the villains on Gao Gai Gar have names that start with the letter P.
 * Jonathan, Joseph, Jotaro, and Joleyne Jostar
 * And the other main protagonists still have their names starting with a "jo" sound, as per the title reference.
 * Naruto has Hisashi, Hizashi, Hinata and Hanabi Hyuuga. Oh, and Neji.
 * There's also the trio of Ino, Shikamaru, and Chouji whose dads' names also start with the same two syllables (Inoichi, Shikaku, and Chouza) as part of their shared theme of being named after Hanafuda cards.
 * This likely applies to the Aburame Clan as well, given the named members (not counting, which is probably an alias) are Shino, Shibi, and Shikuro. Really, it seems the only clans that don't do this are the Uchiha, Senju, and Inuzuka.
 * Rave Master had an interesting example in the Tower of Din arc; if you added the prefix 'Ma' to all of the non-human characters' names, you'd get things like Mallet (Let), Multiangle (L'tiangle), Mothership (Zharshippe), etc.
 * Several characters in One Piece possess the "Will of D", marked by having "D." as a middle initial. They don't know what it stands for, but they all have superhuman strength and willpower and no fear of death. These include the main character, Monkey D. Luffy.
 * In Bizenghast, the vault guardians share the first letter 'e' of their names: Edaniel, Edrear, Eniri and Elala.
 * (Nearly) All of the cast of Aria have names beginning with "A".

Comics

 * Superman's connection to the initials L.L. Started as a coincidence in The Golden Age of Comic Books, became downright creepy in the sillier part of The Silver Age of Comic Books. These include but are not limited to Lois Lane, Lucy Lane, Lex Luthor, Lena Luthor, Lana Lang, Lori Lemaris, Luma Lynai, Lyla Lerrol, Lara Lor-Van, Letitia Lerner, and Lupe Leocadio.
 * Several previous hosts to Plant Elementals in Swamp Thing have names that sound similar to Alec Holland (who, due to a Stable Time Loop, is the template they're all based on). The original Swamp Thing was Alex Olsen, and before him there was Alf Oldland (Jack-in-the-Green) and Alice Huston (Lady Jane). Between Alex and Alec were Albert Höllerer (the Heap), Aaron Hayley (Swamp Thing II) and Alan Hallman (Swamp Thing III). And when the Sprout was looking for a host, it attempted to bond with Alan Bolland, Gary Holland, Alden Hollandaise and Alan Helstrom.
 * Maybe this is why things didn't work out with Cyrus "Solomon Grundy" Gold and he became a giant swamp zombie instead.
 * The Endless from Sandman. Their names all start with D: Destiny, Death, Dream, Desire, Despair, Destruction and Delirium.
 * Unlike most examples, people are aware of this theme. At least three individuals have pretended to be Endless by coming up with pseudonyms that begin with D.

Film

 * The Moopets from The Muppets take the names of the Muppets they are a knockoff of and fit an "oo" into them -- hence, Kermoot (Kermit), Foozie (Fozzie), Miss Poogy (Miss Piggy), Roowlf (Rowlf), Janooce (Janice), and Animool (Animal).

Gamebooks

 * Joe Dever is very fond of giving evil characters, creatures and places names with double A's in them, probably because it looks and sounds harsh and foreign to English speakers. This nuance was likely lost when the books were translated into languages such as Dutch, Norwegian and German, in which double A's are a lot more common than in English.

Literature

 * In the Pit Dragon Chronicles by Jane Yolen, most of the characters have a "double K" in their name (like Jakken or Akki). This is explicitly explained in the text; people with a double-K are slaves or descended from slaves.
 * In A Song of Ice and Fire several members of House Lannister have names beggining with "Ty-": Tywin Lannister, his father Tytos, his brother Tygett, nis nephew Tyrek, and his son Tyrion. Strangely enough Tywin's first son is called Jaime.
 * Likewise, several members of House Greyjoy have names ending with the "-on" syllabe: Lord Balon Greyjoy, his brothers Euron, Victarion, Urrigon and Aeron, his half-brothers Harlon and Quenton, his sons Maron and Theon. There's also a relative called Dagon Greyjoy.
 * The names of House Targaryen are usually some variation of the original three founders: Aegon, Visenya, and Rhaenys, using either the first or second half of the name. Daenerys's son with Drogo is named Rhaego, combining both Targaryen and Dothraki elements.
 * In Kim Stanley Robinson's novel The Years of Rice and Salt, the story follows three major characters who reincarnate many times over the course of many centuries. Each incarnation has the same initials.
 * A particular Stephen King villain uses a variety of names, most with the initials R.F. ("Randall Flagg" being his most famous version). Oddly, though, his real name turns out to be totally different.
 * The villain from Dean Koontz's The Good Guy does something similar, using the initials R. K.
 * Michael Moorcock has a lot of significant characters with the initials J.C., most famously Jerry Cornelius.
 * Characters in the Deverry series often (but not always) have similar names to their previous incarnations. For instance, Jill has been Brangwen, Gweniver, Branoic and most recently Branna, while Rhodry has been Maddyn, Maer and Meddry (interestingly, the incarnations we first meet them in don't seem to be examples - until the final book reveals their earliest recorded incarnations were called Hwilli and Rhodorix). Nevyn spent most of the time period covered by the books as unaging, but in the most recent sequence has been reborn as Neb.
 * In Flowers in the Attic by V.C. Andrews, the Dollanganger children are named: Christopher, Cathy, Cory and Carrie. Their parents are Chris Sr. and Corrine.
 * In the book's sequel Petals on the Wind, Cathy names her son Jory, the "ory" for her brother Cory, but with a "J" for.
 * In the Star Wars Thrawn Trilogy, clones' names are distinguished from the original by doubling a vowel. The two most prominent are Joruus C'baoth and Luuke Skywalker.
 * In The Mortal Instruments, "JC" is a significant pair of initials. It's for Clary's  father Jonathan Clark, her   brother Jonathan Christopher, the latter name of which serves as the basis for Jace's name.
 * And in the prequel trilogy The Infernal Devices there's JTS...
 * John Flanagan, author of the Rangers Apprentice series, said he's tried to avert this. He'll read back through part of a manuscript and realise he gave a bunch of characters names starting with the same letter, so he'll go back and change some of the names.

Live Action TV

 * In Babylon 5, the Shadows seem to like Z sounds as well. Z'Ha'Dum, their homeworld, Entil'Zha, the title of leader of the Rangers, Zha'dam, the machine that made the death cloud (in a novel rather than the show).
 * Entil'Zha, Z'ha'dum and Isil'zha are Minbari words. I'd guess the same is true of Zha'dam. (Zha, loosely speaking, means future.)
 * Babylon 5 also seems quite fond of names that begin with "Dra-". I can think of Drazi, Draal and Drakh offhand, but I'm sure there must be others. I'd put this down to either laziness or a syllable fetish on JMS's part.
 * Speaking of JMS, he was fond of giving his protagonists the same initials as him.
 * Earlier versions of Star Trek actually had this as a canon for Vulcan males -- Spock, Sarek, Sybok, etc. Females got more choice, though initially all of them were some variant of T'(x). (T'lar, T'Pau...)
 * Tuvok in Voyager is an exception, though.
 * The Expanded Universe attempts to cover for this by saying that Surak inspired five-letter names that either start with S or end with K. Furthermore, what with the shortage of Sxxxk names, it's a status symbol. Sarek's house is very prominent, so they still get to use them.
 * Even when the name doesn't end in K, there will often be a K in it. "Sarek, child of Solkar, child of Skon."
 * The Making Of Star Trek reprints a half-serious memo written by Bob Justman suggesting that all Vulcan male names should begin with SP and end with K. At one point it was said that the "S" and "T" prefixes served more or less the same function as "Mr.", "Mrs.", "Miss", etc.
 * The Completely Useless Star Trek Encyclopedia suggests that Tuvok is a hermaphrodite, whereas Saavik's parents really wanted a boy.
 * Originally, at least in TOS, all the Klingon names began with K (Kor, Kang, etc.). Then Worf came along and that all went out the window.
 * Mexican writer, actor, director, comedian, humorist, songwriter, poet and philosopher, Roberto Gómez Bolaños, best known as Chespirito, was rather fond of this trope. He was the man behind the incredibly popular El Chavo del Ocho and El Chapulín Colorado television shows, portraying the eponymous protagonists in both. Other characters created by him are la Chilindrina, el Chanfle, el Chómpiras, el Dr. Chapatín, la Chimoltrufia, Chaparrón Bonaparte and los Chifladitos. Words and phrases frequently employed in his shows include “¡Me lleva el chanfle!”, “¡Se me chispotéo!”, "¡Chusma, chusma!", “La vieja chancluda”, "Huesito, huesito de chabacano", “"¡Matanga, dijo la changa!”, “El Chipote Chillón”, “Chiquitolina”, and “Chiripiorca”. Can you tell a pattern?
 * In Dollhouse, the names of actives follow the letters of the NATO phonetic alphabet (So far we've seen Alpha, Charlie, Echo, Mike, November, Sierra, Tango, Victor, and Whiskey). Note that these names are artificial codes, however; for example, Echo's "real" name is Caroline, November is Madelaine, Sierra is Priya, etc.
 * The actives in a second house are named after Greek Gods.
 * About 99 percent of the evil immortals in Highlander have names that begin with a K, a hard C, a Ch or rarely, a Q.(Quentin Barnes in the series, though Quentin in the animated series is a hero, not a villain.)

Video Games

 * In Final Fantasy X, the Besaid Aurochs all have a double letter in their name. Wakka, Botta, Keepa, Jassu, Letty, Datto...and Tidus (if you're using his Canon Name, at least).
 * Considering Tidus was originally from the Zanarkand Abes and not the Besaid Auroch's, he might not really count.
 * In Homeworld, just about every name of relevance has a K in it. Kharak, their homeworld, Kadesh, the home of their insane brothers, Kushan, the name of the exiles, Khar Selim and Khar Toba, the names of a support vessel and the generation ship that brought them to Kharak respectively, and Karan Sjet, the voice and mind of the Mothership.
 * Indigo Prophecy gave most of the main characters a K or C in their name. Markus, Carla, and Lucas Kane.
 * In Kingdom Hearts, all members of Organization XIII have an X in their names. Initiation into the Organization actually requires an X to be added to the letters of the member's previous name.
 * In the War Craft universe, the color and gender of a dragon usually determines the end of their name. Red dragons tend to have names ending in "-asz" or "-asza", blue dragons ending in "-gos" or "-gosa", etc. This has caused some debate when a visibly female bronze dragon character had a name that ends in the masculine "-ormu" (rather than "-ormi").
 * In Gungrave, a number of Syndicate members have names starting with B: Brandon Heat, Big Daddy, Bear Walken, Bunji Kugashira, even Beyond the Grave.
 * There has yet to be a Kremling whose name does not include the letter "K", usually as the first letter in a homophone of a word that contains a "C". (ex. K. Rool, Kritter, Krusha, Klaptrap, Kalypso, Kopter, etc.)
 * For the Kongs, we have: Donkey, Diddy, Dixie, Cranky, Funky, Candy, Kiddy, Chunky, Tiny, Lanky, Swanky, Wrinkly and Bluster.
 * The names of the three main characters in The Combatribes all begin with the letter "B" (Berserker, Bullova, and Blitz).
 * Delivery Missions in Billy vs. SNAKEMAN are based on the 11 Ds, a collection of stats that all begin with D, like Drive, Deliciousness, and Dancing D-Speed.
 * Bug! had the 6 levels, four of which ended with -ia (Insectia, Reptilia, Splot, Quaria, Burrubs and Arachnia).

Toys

 * Bionicle bad guys almost always have an "ak" sound in their names: MAKuta, rAHKshi, BohrOK, PirAKa, and so on. This is partly because the names need to sound foreign and hard K sounds are easy targets.
 * A better example is that each tribe of Matoran has a syllable representing its element. For example the fire Matoran are the "Ta-Matoran", a Toa of Fire is Tahu, and fire Bohrok are Tahnok. Rahkshi and Visorak also reference it even though they don't have elemental affiliations; continuing the previous example red Rahkshi are Turahk (close enough) and the red Visorak breed are Vohtahrak.

Web Comics

 * In Eight Bit Theater, we see that all Pronteran children are given names beginning with the letter P, such as Penny, Peter, Paul, and Pjoe.
 * In Gunnerkrigg Court, the names of the three most important locations in Antimony's life all start with G: the titular court, Good Hope Hospital, and Gillitie Wood. Don't know if that's just a coincidence or what.
 * In Everyday Heroes, Mr. Mighty and his two brothers are Marion, Michael, and Morrison.
 * Also, the neighborhood moms are Jane, Joan, Jenny, Ginny, June, Jan, and Jin; the single dads are John and Jean (French).
 * All of the Freakangels have a hard 'k' sound in their name.
 * Homestuck's main four share initials with their ectobiological ancestors; all of the have names beginning with.

Western Animation

 * In Avatar: The Last Airbender, the Fire Nation loves their Z's: Sozin, Azulon, Ozai, Azula, Zuko, Kuzon, and Zhao, although that's not a hard z like the others. The Water Tribe, on the other hand, is all about K's: Kana left Pakku and had Kya who married Hakoda and had Sokka and Katara.
 * The Powerpuff Girls (they all start with B). Oh, and don't forget the Rowdyruff Boys and Powerpunk Girls.
 * South Park has the McCormick siblings, whose names all start with "K"; Kevin, Kenny, and Karen.

Real Life

 * The Duggar family, who gave all 19 of their kids names starting with J. This led to names like Jinger. Go ahead, take a guess at the pronunciation.  This started out by coincidence, then when the Duggars realized the trend, they did not want to have a child who was the odd one out and then they kept having kids... However, that does not explain why they used Jinger before they used Jennifer (to Jennifer Duggar's future relief).
 * Still better then Apple, Zuma, and Moses.
 * Former US President Lyndon B. Johnson liked his initials so much that not only did he enjoy being known solely by them (LBJ), but married Claudia, who self-titled herself "Lady Bird," later becoming Lady Bird Johnson, and named his two daughters Lynda Bird Johnson, and Luci Baines Johnson. If that wasn't enough, during office, he also had a beagle named - you guessed it - Little Beagle Johnson. Among other pets he blessed with his initials.
 * Robert Rodriguez' children Rocket, Racer, Rebel, Rogue, and Rhiannon.
 * Sylvester Stallone's sons all have names beginning with S. When he named his daughter Sistine Rose, his mother kidded him for naming his child after a place he'd never been to just because he liked the sound.
 * Prince Michael Jackson, Paris Michael Jackson (girl), and Prince Michael Jackson II (AKA "Blanket" AKA "OMGDONTDROPHIMYOUCRAZYMANCHILD"). Guy ran out of ideas pretty quickly.
 * Kris Kardashian and her daughters Kim, Khloe, Kourtney... their brother's name is Robert, after his dad. Their stepfather is Olympian Bruce Jenner (seriously) and his sons are named Burt, Brandon, and Brody. Their sister is Casey, and everyone's half-sisters are Kylie and Kendall (phew!).
 * If anybody actually cared we'd need a diagram.
 * Are they from GuadalaKHHHHHHHHHara?
 * In the Germanic tribes back in ancient and viking times, all the sons in a well-to-do family normally had names starting with the same letter as their father's. This is because the rhyming schemes of their poetry was based on how words start, not on how they end, and the most highly regarded verse form has a rhyme every four syllables! So, if you want a nice, rhyming song on everything you achieved in life, it is certainly helpful if your sons have names that already rhyme.
 * The German noble house of Reuss took this one step further: every single male son has been named Heinrich (Henry) for centuries, originally to show its devotion to a medieval king of that name. In fact, the house was known as the "house of Heinrichs" before it gained the name Reuss (after a small principality in Thuringia). There are two lines (elder and younger), both number their sons separately by order of birth, one starting anew with I when the number LXXXXIX (99) is reached, the other starting fresh at the beginning of each century. In everyday conversation, the various Heinrichs also keep each other apart by using different diminutives (Heinz, Heini) or foreign forms (Henri, Harry) of the name.
 * Bach named two of his sons Johann and a daughter Johanna.
 * Although that is likely to be at least partly coincidental. It was just that people used fewer first names in the 18th century, and children were also frequently named after their godparents. "Johann/Johannes" in particular was one of the most commonly used ones, both in Protestant and Catholic regions.
 * All kings of Prussia were named Frederick (Friedrich) and/or William (Wilhelm), starting with Frederick I (formerly elector Frederick III of Brandenburg, son of Frederick William, the Great Elector) and ending with William II (whose crown prince was also called William). Besides three Fredericks and two Williams, there were four kings called Frederick William.
 * In the 1960s and 1970s, the US Senate played host to the truly epic career of Majority Leader Mike Mansfield (and his wife Maureen) of Montana.
 * A vehicular version: All of the gunships used by the United States Air Force (basically heavily gunned attack planes converted from cargo transports) have names starting with S. AC-47 Spooky, AC-119G Shadow and AC-119K Stinger, and the AC-130H Spectre and AC-130U Spooky II, and the AC-27J Stinger II.
 * An odd unintentional one. Many people who work on Atop the Fourth Wall have a name starting with L. There's Lewis Louvhaug, who took on the name Linkara and who's bum character is named Lester (a theme naming for another time). Then there's Lewis's father who has played several characters that would be too old for Linkara's range (Teens to early thirties) who is credited as L. Lovhaug. Then there's his ex-girlfriend (Iron) Liz, the actor for female characters. And apparently Liz from another world is called Lita Liz instead of Iron Liz.
 * After the Seven, all cars made by Lotus have had names starting with "E". (Elan, Elite, Europa, Esprit, etc.) The Carlton was a modified Vauxhall.
 * Ford Motor Company did this for a little while with the both the Ford (Focus, Five Hundred, Fusion, Flex) and Mercury (Montego, Mariner, Mountaineer, Milan) brands.
 * The Laeisz shipping line of Hamburg, which continued to use sailing vessels after most others discontinued them, was better known as the Flying P Line after its practice of giving all its ships names beginning with the letter P (the first was the Pudel (= poodle)). The line's windjammers included the five-mast Preussen, the tragically sunk Pamir, its sister ship, and the Padua (seen in the film Die Große Freiheit Nummer 7). The Passat (= Passaic wind) is now a museum ship in Travemünde, while the Peking can be seen at South Street Seaport in New York.
 * Many classes of warships of the Royal Navy were given names beginning with a particular letter, thus in World War Two it had 'D' and 'E' class cruisers (the latter consisted of just two ships, the Emerald and the Enterprise), destroyer classes going from 'A' to 'Z' (leaving out X and Y, but having 'V' and 'W' twice, the first ones built during World War One) and 'S', 'T' and 'U' class submarines.
 * A few of their nuclear platforms had names starting with 'V'. The Royal Navy has the four Vanguard class submarines (Vanguard, Victorious, Vigilant, and Vengeance) and the RAF had the V-bombers (Vulcan, Victor, and Valiant).