* ActingForTwo: Paul Mercier provides the voice of both Leon and the Merchant, so he's not only talking to but also buying and selling things to himself.
* BadExportForYou: Due to Germany's [[MediaWatchdog youth protection laws]], the German version of the game is missing the Assignment Ada and The Mercenaries minigames. It's also ''brutally'' trimmed down in terms of violence, to the point that German gamers resorted to the loophole of importing the uncensored and German-speaking Austrian version instead.
* ColbertBump: A minor example for the Zeebo. This Brazilian video game console would've likely flown under the radar internationally had ''Resident Evil 4'' not had a port for it. The port is essentially another point in favor of the game's PortOverdosed status.
* {{Defictionalization}}: One company produces handmade replicas of both [[https://traditionalarcherybows.com/handmade_resident_evil_knife_influenced_by_resident_evil_4_p111.html Leon]] and [[http://traditionalarcherybows.com/handmade_jack_krauser_knife_resident_evil_4_p105.html Krauser's]] knives.
* FollowTheLeader: This game was hugely influential on a number of other games that followed it, including ''VideoGame/DeadSpace'', ''VideoGame/GearsOfWar'', ''VideoGame/DarkSector'', and many others.
* MilestoneCelebration: ''Resident Evil 4'' was re-released for the Xbox 360 and [=PlayStation=] 3 alongside ''VideoGame/ResidentEvilCodeVeronica'', ''VideoGame/ResidentEvilTheMercenaries3D'', ''VideoGame/ResidentEvilRevelations'', and ''VideoGame/ResidentEvilOperationRaccoonCity'' during the 15th Anniversary of the ''Resident Evil'' franchise. The game later received an HD remaster for Xbox One and [=PlayStation=] 4 during the 20th Anniversary of the franchise along with ''VideoGame/ResidentEvil5'', ''VideoGame/ResidentEvil6'', ''VideoGame/ResidentEvil0'', and ''VideoGame/ResidentEvilRemake''.
* NoExportForYou: The Platform/NGage port was released only in Japan, the Zeebo port was released only in Brazil (as the console itself was only released there, despite being developed in America), and the Android version was released only in Korea outside of very few Samsung phones through its own store at the time of release.
* PlayingAgainstType:
** Carolyn Lawrence is known as the voice of Sandy Cheeks of ''WesternAnimation/SpongeBobSquarePants''. Here, she's in a gritty survival action horror game as Ashley Graham.
** Creator/RinoRomano is best known for his roles as Batman in ''WesternAnimation/TheBatman'' and Randy Hermandez in ''WesternAnimation/GodzillaTheSeries''. Here, he plays the scientist Luis Sera.
* PortOverdosed: Despite its "Only for [[Platform/NintendoGameCube GameCube]]" label in its original release from 2005, the game has been ported to Platform/PlayStation2 (months later after the [=GameCube=] version), the N-Gage (2005), PC (2007, a PortingDisaster), Platform/{{Wii}} (2007), Zeebo (2009), Apple [=iOS=] (2009), Platform/PlayStation3 and Platform/Xbox360 (2011), Android (2013), PC again (2014, a PolishedPort), Platform/PlayStation4 and Platform/XboxOne (2016), Platform/NintendoSwitch (2019), [[Platform/OculusQuest Quest 2]] (2021), and remade for the [=PlayStation 4=], Platform/PlayStation5, Platform/XboxSeriesXAndS, and PC, a total of 17 ports and counting. It has seen releases across four generations of video game hardware and the only major platforms that never got a version of the game in its lifetime were the Platform/{{Xbox}} (which is probably due to Creator/{{Microsoft}} all but abandoning the system in 2005 in anticipation of the then-coming 360) and Platform/WiiU (which still ended up getting the ''Wii Edition'' ported to its version of the eShop, though the game still had to be played in Wii Mode).
* PromotedFanboy: Albert Marin, one of the lead developers behind the HD Project for ''resident evil 4: Ultimate HD Edition'' on Steam, was [[https://www.re4hd.com/?p=9693 hired]] by Creator/NightdiveStudios in 2023.
* ReferencedBy: The Merchant in ''VideoGame/DustAnElysianTail'' is a takeoff of everyone's favorite friendly Ganado. Fidget even jokes that he'll "[[BriefAccentImitation Buy it at a hoigh proice!]]" in reference to samples of ItemCrafting materials.
* RoleReprise: Sally Cahill reprised her role as Ada Wong.
* SavedFromDevelopmentHell: Counting the early proposal that became ''VideoGame/{{Devil May Cry|1}}'', ''Resident Evil 4'' was in development for at least half a decade. The premise was changed several times in this timeframe.[[note]]From fighting zombies, to mist enemies, to the puppet humans in the final version.[[/note]]
* SequelGap: The game was released six years after ''VideoGame/ResidentEvil3Nemesis''.
* WhatCouldHaveBeen: Before the developers settled on what would become ''[=RE4=]'', they went through several prototype versions of the game, which are collectively known as ''Resident Evil 3.5'':
** Development on the first iteration of the game overlapped with that of ''[=RE3=]'' (back when that game was still considered to be ''Resident Evil 1.9''), predating Creator/ShinjiMikami's decision to switch to the [=GameCube=]. According to an interview with [=1UP=].com, Creator/HidekiKamiya claims that, initially, this was to be the third ''RE'' game instead of the one that came out. He is likely referring to the game featuring HUNK on a cruise ship, being called ''[=RE3=]'' at the time Kamiya worked on it - and before the number went to the game with Jill and Nemesis. That "''[=RE3=]''" that Kamiya worked on barely got past concept phase before being scrapped, and his team moved on to the next project, which is known as the first version of ''[=RE4=]''. The cruise ship version of ''[=RE3=]'' got revisited twice: once with the non-canon ''VideoGame/ResidentEvilGaiden'', the second with the fourth ''VideoGame/ResidentEvilGunSurvivor'' game, ''Resident Evil: Dead Aim''.
** An earlier version of the story was going to deal with the ending of ''Resident Evil Gaiden'', which showed a B.O.W. disguised as Leon to be later confronted. However, changes to the game later resulted in ''Gaiden'' being non-canon.
** The "Biohazard 4 2000" build, internally referred to as the "Stylish version", featured a superhuman private investigator named Tony Redgrave as the protagonist, with him and his twin brother Paul being the Progenitor Virus-mutated sons of Earl Oswell Spencer. Tony was a superhuman cop that would explore and fight throughout the hidden Umbrella base of Mallet Island, its castle and the lab facility beneath it. Its development included several trips to Spain and England to study castles as the inspiration for the environments. This game was deemed to be too great a departure from the SurvivalHorror genre, and would be {{retool}}ed into ''Devil May Cry''. While the game's setting remained unchanged (other than Mallet Island becoming more supernatural), Tony and Paul became Dante and Vergil, the B.O.W.s became demons and Earl Spencer's role was split into two separate characters: Sparda became the twins' father, and Mundus took his place in the story as the BigBad.
** Following this was the [[https://www.youtube.com/watch?v=LG_AAkg-lJc "Castle Version"]] (also known as the "Fog Version") on the [=GameCube=], whose premise involved Leon infiltrating Umbrella's European headquarters, getting infected with an at-the-time undecided virus and fighting fog-like creatures that may or may not have been [[ThroughTheEyesOfMadness the creations of his collapsing, virus-corrupted sanity]]. One of the levels was to take place on [[CoolAirship an airship]], and the game would've potentially ended with Leon dying of the virus, a move that was unpopular with the developers and a minor reason to why the version was scrapped. The major ones were problems with the hardware not being powerful enough and the game being too expensive to make.[[note]]The final version is noticeably graphically inferior to this version.[[/note]] The seemingly supernatural nature of the hallucinated enemies was also something that was debated internally at Capcom, as it didn't really fit the series.\\
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This version was also supposed to have two big reveals: the origin of the Progenitor virus and the depiction of Albert Wesker's HCF assault against Umbrella. Wesker's assault has never been depicted in the series, since it was brainchild of late series scenario writer Noboru Sugimura and Capcom felt it wasn't right to depict it without his input. The Progenitor virus, rather than being found in the "Stairway of the Sun" flowers depicted in ''VideoGame/ResidentEvil5'', was to originate from ancient human remains found by archaeologists exploring the castle, with the founding being what gave Spencer the ambition to begin his virus research. There was also a sideplot involving a woman accompanied by a B.O.W. dog exploring said castle. After this version was scrapped, Sugimura donated the scenario to Capcom Production Studio 3, who removed Leon from the equation and turned it into ''VideoGame/HauntingGround''. [[spoiler:The hallucinated enemies]] concept would later appear in ''VideoGame/ResidentEvil7Biohazard''.
** After that version was scrapped, Capcom made various short gameplay tests to decide the path that the next version would take. These gameplay tests included the [[https://www.youtube.com/watch?annotation_id=annotation_326592&src_vid=kWpEE_5pDzQ&feature=iv&v=k8nKcMwmt3I "Hooked Man Gameplay,"]] which had the same basic gameplay as the previous Castle Version and reused assets, such as the mansion environment, from the previous version to showcase the gameplay. It featured Leon exploring a haunted mansion with his biologically modified dog sidekick, while fighting what appeared to be paranormal enemies, such as medieval suits of armour,[[note]]Which would make it into the final version, albeit not in a paranormal form[[/note]] living dolls, a mounted deer head which jumped off a wall and attacked, and the titular, ghost-like "Hooked Man", a possessed-looking chap who wielded a giant hook on a chain.\\
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The [[PressXToNotDie quick time events]] and AlwaysOverTheShoulder camera angles used in ''RE'' games from ''4'' onward first appeared here. It alternated between the "classic" fixed cameras when exploring and the OTS camera when aiming. It also featured a mechanic where [[VideoGame/AlanWake shining a flashlight]] on the Hook Man enemy made it slow down and vulnerable to damage from firearms. The effect from this mechanic is still in the demo of the final version, despite not actually being used. Capcom decided to not go further with the Hooked Man gameplay test due to largely the same reasons the previous Castle Version was scrapped. The Hooked Man test is also not fondly remembered by at least one lead designer on it, due to not being very original.
** The last version before the released one reportedly featured zombies again and was discarded for being too formulaic. It was known as the "Umbrella Takedown" version, and would've continued on from ''VideoGame/ResidentEvil2'', ''3'' and ''[[VideoGame/ResidentEvilCodeVeronica Code: Veronica]]''[='=]s endings about the main characters taking on Umbrella.
** It seems fairly obvious that the Chicago Typewriter was, at one point, envisioned as a standard weapon as it comes with maxed-out stats (as opposed to being explicitly overpowered; the stat bars even indicate it has an Exclusive upgrade installed by the gold, 10.0 "Firepower" stat) and has a reload animation despite having BottomlessMagazines (as the [=PlayStation=] 2 version came later, they took advantage of this and gave it a unique animation when Leon attempts to reload it while wearing the mafia costume). This is likely because too much of its function overlaps with the TMP to make it worth adding to the standard lineup but the RuleOfCool factor of being able to wield the iconic submachine gun was too great to cut it out entirely.
** Right before they settled in [[SuspiciouslySpecificDenial Not Spain]], the game location was a village in [[{{Ruritania}} Eastern]] [[{{Uberwald}} Europe]]. This would later be revisited in ''VideoGame/ResidentEvilVillage'', which also takes several design cues from ''4''.
** Among the content cut from the version of the game that was released, a few files were cut out of the game. Among these files was one that revealed that Del Lago was an ancient mutant from the time before the first castellan sealed away the Las Plagas.
* WritingByTheSeatOfYourPants: The game was written by Shinji Mikami in just [[https://www.vg247.com/shinji-mikami-hopes-a-resident-evil-4-remake-will-make-his-story-better three weeks]], which likely accounts for the somewhat bizarre DenserAndWackier storyline.

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