Development Hell: It's largely forgotten by now, but The End of Evangelion was in this for a brief period, which is why so many Japanese viewers who went to see Death and Rebirth were pissed off at the sudden cut-off of an ending. There's also the live-action movie (a co-production between Studio Gainax, ADV Films and WETA), which has allegedly been "in pre-production" since 2003. Rebuild of Evangelion also counts; 2.0 was delayed a full year after its original release date, and 3.0's is around three years after 2.0's. Keep in mind that the tetralogy was supposed to be finished by now.
Enforced Method Acting: Yuko Miyamura allowed herself to be strangled by Megumi Ogata in the recording room during Shinji's vision of strangling Asuka in End of Evangelion.
One of many theories regarding how the final episodes came to be as notoriously bizarre as they are is that the original scripts for the last two episodes were rejected by the network due to their graphic content; thus the current ending was made due to last-minute budget cuts and/or as a way of giving the network the finger, and the rejected scripts eventually became The End of Evangelion.
Lying Creator: The amplitude of self-contradictory and at times seemingly absurd statements about the series from Hideaki Anno has led many to accuse him of this.
The Other Marty/The Other Darrin: While the Japanese cast has remained remarkably consistent over the years, the English dub is notorious for being recast with every subsequent iteration of the series (four so far, for those keeping track). Most characters have had between two and four different voice actors, with poor Toji having at least six. The only characters who have retained the same voice between every version so far are Shinji, Misato and Asuka.
It's even worse in the Spanish dub, in which Shinji is the only character in retaining voice actor through the franchise.
There's also the manga. We have several Does This Remind You of Anything? moments, Kaworu killing a kitten, Shinji saying emphatically "Guys don't like guys!", Shinji and Kaworu's relationship downgraded to an unrequited Stupid Sexy Flanders, Kaworu calling Rei a fool and saying "I figured you'd be a heftier girl.", Shinji and Kaworu in the ladies' room with Asuka... yeah.
Schedule Slip: The manga, and how. The first chapter was released months before the anime started (December 1994), but the last chapter was published in June 2013. That's over 18 years for 14 volumes of material!
Short-Lived Big Impact: Evangelion was one of the most influential anime shows of the Giant Mecha Genre and in general, but only lasted one season and 26 episodes.
Shrug of God: After fans were upset with the ambiguity of the series, Hideaki Anno basically declared that it was up to viewers to determine their own meaning and reprimanded them for expecting all the answers on a silver platter. Over the years he has offered, at best, several vague and contradictory statements as to the meaning(s) and intentions of the series.
Technology Marches On: Back in the series' heyday in the mid-to-late 90s, Shinji listened to his music on an S-DAT player. Nowadays, with the sporadic manga releases, it's been replaced by a Mini iPod.
While Apple still makes very small MP3 players, the product officially named "iPod Mini" has been retired.
The show began after Anno suffered from a clinical depression, and relied on several sponsors for its support. Several of these sponsors pulled out as the show became increasingly dark. Given that this was before Evangelion became a Cash Cow Franchise, it's a wonder that Anno and Gainax got the show finished.
This trope also extended to the American side of the Pacific with ADV Films. Commentary for the English dub will often make reference to it being made on budget that consisted of a metaphorical shoestring and paperclip, involved renting out space to do recordings with substandard equipment, and had a good portion of the cast played by members of the production team besides the voice actors, among other things. They weren't exactly in danger of going out of business, but it's still pretty amazing that the dub was as good as it was all things considered.
The Mexican Spanish dub suffered of this, big time: Originally it was planned to be dubbed with a different voice cast. For some reason, the licesor (Possibly ADV Films) decided to dub the series in Colombia, using the same studio who dubbed the very unpopular dub of Rurouni Kenshin. For unexplained reasons, they only dubbed a pilot episode, but they were never be able to dub the entire series. Later, the dub as planned to be made in a Spanish-speaking studio in Los Angeles and, after too much criticism, it went back to Mexico again, albeit with a very different cast from the original Mexican one.
On a meta level, Anno attempted to recruit Kunihiko Ikuhara for the series and even named Rei Ayanami after Sailor Mars in an attempt to lure him in. Had Ikuhara agreed, the show would likely have had even more surrealism thrown in.
In End of Evangelion the live-action sequence was supposed to be much longer, with an older Asuka, Rei and Misato played by their voice actors (the sequence was included in the Japan-only Renewal release as an extra).
There are a total of 28 Angels; the document uses the same Japanese word as in the series but also includes "Apostolo" in katakana. In order to get the extra twelve/thirteen out of the way quicker, the twelve strongest ones were supposed to have attackedall at once during the finale, completely erasing America from the map.
The Evas look slightly different. Units 05 and 06 are specifically mentioned; Unit 05 was to have been brought into Japan after Zeruel while Unit 06 would've perished during the finale. While not making it into the series, these Evas were recycled for the Rebuild movies as the personal Units of Mari and Kaworu respectively.
Ritsuko is a fan of bonsai and punk rock, of all things.
Hyuga, Ibuki and Aoba aren't present and SEELE isn't mentioned. There is however mention of a character named Conrad Lawrence; based on the description of him being an old man who set up NERV and put his later nemesis Gendo into position, he might've been the earliest draft of Lorenz Keel.
Sketchy descriptions of the final episodes taking place differently: after Rei's secrets are revealed, the twelve strongest Angels descend from the Moon and completely annihilate America, destroying Unit 06 in the process and plunging humanity into mass panic. The UN decides they have nothing to lose and aborts the Human Instrumentality Project over Gendo's protests, resolving to go down fighting instead. A cryptic mention of "the ruins of Arka, the Promised Land" (located in the Geofront) being a key objective.
Kaworu mentioned without name as a child with a cat. To those who have read the manga, this sounds even weirder. According to interviews with Anno the cat would have made it into the final product had it not been for budget-constrains. The same interviews also reveal that they had at one point considered introducing Kowaru earlier than they eventually did and that Shinji first would have found him playing an abandoned piano in some a ruined house.
Arael was supposed to have engaged the Evas in close aerial combat instead of Mind Rape, using some sort of vibroweapon on its wingtips. The Evas themselves would've been equipped with flight harnesses in order to fight the Angel. These plot elements both found their way into the third Rebuild movie.
Shinji was supposed to have received the Mind Rape (from an Angel unrelated to Arael), not Asuka.
Dub-related: According to the commentary, Amanda Winn Lee originally wanted to try out for the role of Misato, before Allison Keith's performance changed her mind.
Kaworu was originally going to be a transfer student at the kids' school, rather than the newest Evangelion pilot. This was changed after Hideaki Anno realized that the school setting had more or less been written out of the show by the time episode 24 came around.
What would the later episodes have been if they had had the money? What is clear is that End of Evangelion was basically an expanded version of what was originally scripted for the final two episodes, hence the film being split into two parts. Had Gainax's budget not been shot, the finale would have just been a shorter version of the movie (albeit with less sexual imagery.)
Shinji was supposed to have longer hair that would wave in the wind and that he could hide behind during dramatic scenes. They cut his hair because he looked too feminine and too messy.
The plug suits would look closer to the classic space suit look, Rei was initially dubbed Yui Ichijo, had black hair, got along better with Asuka and was friendlier and less the Rei Ayanami Expy we know today.
Initially the final line of End of Evangelion was going to be "I won't let you kill me" rather than the infamous "I feel sick". (The original scrip for Episode 26 had the line be proceeded by a trademark "baka!"/"idiot!", but it was removed from EoE's storyboard). According to Yuko Miyamura (Asuka's voice actor) Anno couldn't make her say it how he wanted it to sound, eventually he instead described the masturbation scene to her from Asuka's perspective and had asked how she would react if it happened to her, which led to the current line.
The leaked original script for episode 25 and 26 (which was used for the End of Evangelion) featured two different proposed epilogues, neither of which corresponded completely with the one in film: The first one (Last A) is the closest to the final one, but lacked the Book Ends Lilith/Rei, had the cast's names on the graves Shinji raised, showed Asuka kicking down hers (it is still shown to have been toppled in the final film after she returns from instrumentality) and has the original version of the final line (see above). The second one (Last B) however was much bleaker than the final film. It starts with Shinji laying on the beach holding Rei's hand before Shinji turn his head to see the Book Ends Lilith/Rei. The camera then pans out to show that Shinji is only clutching the arm Rei lost earlier. His monologue then reveals that he was the only human self-reflective enough to ever return from instrumentality, meaning he will be spending the rest of his life alone after finally finding the will to live with other people. After the credits starts both would have shown scenes revealing that Unit-01 had ended up on the moon, its/her helmet broken and revealing woman's hair.
Published drafts for episode 24, as well as the previously mentioned ones for episode 25+26/EoE, shows that there had been plans to include a minor sub-plot about different characters visiting Toji in the hospital that eventually was cut.
Several planned plot elements after episode 16 had to be cut because of their unforeseen similarities to the sarin gas attack on the Tokyo subway in March 1995.
Many of the characters were named after various WWII-era naval vessels; most of them were sunk rather than surviving the war. Katsuragi, Akagi, and Soryu were all aircraft carriers; Akagi and Soryu were part of the Pearl Harbor attack, and sunk at Midway. Katsuragi was completed so late it never actually operated aircraft, but survived the war and was scrapped. Ayanami ran troops to Guadalcanal, but was destroyed by the battleship USS Washington during the climatic naval battle of the campaign. Kirishima was a battlecruiser converted to a fast battleship, and it fell in the same engagement as the Ayanami as another victim of the USS Washington; while Hyuga was converted into a battleship-carrier hybrid and survived into 1945 before carrier aircraft sank it in the Inland Sea. Ibuki, Maya and Aoba are names of heavy cruisers; the Ibuki existed only on paper, it was never built. Maya made it until 1944 before being torpedoed and sunk by the submarine USS Dace in the opening round of Leyte Gulf, while Aoba lasted until 1945 only to suffer the same fate as Hyuga. Langley is also the name of an American aircraft carrier which was sunk by the Japanese off Java (though it wasn't operating as a carrier at the time), and the Graf Zeppelin is the name of an uncompleted Nazi-German aircraft carrier which was sunk as a target by the Russian Navy after the war. Along the same theme, Ikari means "anchor."
Katsuragi was also one of Japan's very last operational aircraft carriers, surviving mostly through delayed construction. All the other ships lending their names to characters, including the first Langley were either sunk in battle or never completed.
At an almost esoteric level, the Akagi was also the name of a Russo-Japanese War-era Maya-class gunboat. How quaint.
See also the similar fates of the Hyuga and Aoba, both in reality and in Evangelion; it's even tempting to try and draw some parallels between Mana and Rei's fates and the fact their namesakes were both lost in the same battle.
The Ayanami bears mentioning that not only is it the name of a destroyer; it means "wave pattern" as in "frequency." Similarly, Shikinami (from Rebuild) literally means "wave equation," as in "wavelength." If we combine these two together, we get the equation for the speed of light. This allows for Fridge Brilliance: Both Rei and Asuka were designed to be two parts of the same whole.
Uh, no. The "wave name Destroyers (other classes had poetic wind "kaze" names) are poetic descriptions, not scientific terms. Ayanami is literally "wave like brocaded cloth", Shikinami is "following wave".
When the kanji for nami (波) is placed behind maki (真希), this will literally mean "wave winding", which can reference "momentum" and/or "velocity". In turn, this relates over to the speed of light mentioned earlier, in which light is found to have both mass and velocity in the form of an electron/photon. For comparison to this "speed of light", her personality (as it is on the Characters page) is most often described as a hard-hitter who normally presses Berserk Buttons on the battlefield.
The second variant is when the kanji for unusual(!) (which is 希) is removed from the above. This new term (波真, which is now nami shin) now has an entirely new meaning: True Wave. This would be best represented by how, near the ending of Rebuild 2.0, Makinami unleashes an entirely new form of the EVA. She explains this as a pilot "rids itself of its humanity", and she uses a code word to unlock this new form: The Beast. Note that the Angels are, as per NERV's research, supposed to bear a 99.89 percent similarity to humanity. That research, along with the above information, makes this "Beast" form not a coincidence.
On another note, the interconnecting theme to the pilots here is how they have some usage of the equation for momentum of light used in Chemistry(!) and other sciences. Applying Fridge Logic based on the above given information, we have (in SI Units): Makinami (representing momentum, in kg*m/s) = Ayanami (representing frequency, in "1/s") x Shikinami (representing wavelength, in "m") x Shinji (representing mass, in "kg"; remember his name literally means anchor).
The Evangelions were based visually on Go Nagai creations Devilman and Mazinger Z. Anno cites the terrifying face, slender build, hunched back and chest plate as coming from Devilman, while its glowing eyes with the red markings were derived from Mazinger Z. The first shot of Evangelion, with its large head, was a direct homage to the first episode of Mazinger Z.
The opening shot of The End of Evangelion is a mirror image of the closing shot of Evangelion: Death. The opening shot of Rebuild of Evangelion 1.0 is a reflection of the closing shot of The End of Evangelion, with a few... scenery details removed.
The US voice actors for the three main Children all married the original voice actors for the Bridge Bunnies: Amanda Winn Lee (Rei) is married to Jason C. Lee (Aoba); Spike Spencer (Shinji) was formerly married to Kendra Benham (Ibuki); and Tiffany Grant (Asuka) is married to Matt Greenfield (Hyuga).