- Acting for Two: 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.
- Bad Export for You: Due to Germany's 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.
- Colbert Bump: 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 Port Overdosed status.
- Defictionalization: One company produces handmade replicas of both Leon and Krauser's knives.
- Follow the Leader: This game was hugely influential on a number of other games that followed it, including Dead Space, Gears of War, darkSector, and many others.
- Milestone Celebration: Resident Evil 4 was re-released for the Xbox 360 and PlayStation 3 alongside Resident Evil – Code: Veronica, Resident Evil: The Mercenaries 3D, Resident Evil: Revelations, and Resident Evil: Operation Raccoon City 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 Resident Evil 5, Resident Evil 6, Resident Evil 0, and Resident Evil (Remake).
- No Export for You: The N-Gage 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.
- Playing Against Type:
- Port Overdosed: Despite its "Only for GameCube" label in its original release from 2005, the game has been ported to PlayStation 2 (months later after the GameCube version), the N-Gage (2005), PC (2007, a Porting Disaster), Wii (2007), Zeebo (2009), Apple iOS (2009), PlayStation 3 and Xbox 360 (2011), Android (2013), PC again (2014, a Polished Port), PlayStation 4 and Xbox One (2016), Nintendo Switch (2019), Quest 2 (2021), and remade for the PlayStation 4, PlayStation 5, Xbox Series X|S, 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 Xbox (which is probably due to Microsoft all but abandoning the system in 2005 in anticipation of the then-coming 360) and Wii U (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).
- Promoted Fanboy: Albert Marin, one of the lead developers behind the HD Project for resident evil 4: Ultimate HD Edition on Steam, was hired by Nightdive Studios in 2023.
- Referenced by...: The Merchant in Dust: An Elysian Tail is a takeoff of everyone's favorite friendly Ganado. Fidget even jokes that he'll "Buy it at a hoigh proice!" in reference to samples of Item Crafting materials.
- Role Reprise: Sally Cahill reprised her role as Ada Wong.
- Saved from Development Hell: Counting the early proposal that became Devil May Cry, Resident Evil 4 was in development for at least half a decade. The premise was changed several times in this timeframe.note
- Sequel Gap: The game was released six years after Resident Evil 3: Nemesis.
- What Could Have Been: 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 Shinji Mikami's decision to switch to the GameCube. According to an interview with 1UP.com, Hideki Kamiya 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 Resident Evil Gaiden, the second with the fourth Resident Evil: Gun Survivor 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 Survival Horror genre, and would be retooled 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 Big Bad.
- Following this was the "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 the creations of his collapsing, virus-corrupted sanity. One of the levels was to take place on 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 seemingly supernatural nature of the hallucinated enemies was also something that was debated internally at Capcom, as it didn't really fit the series.
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 Resident Evil 5, 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 Haunting Ground. The hallucinated enemies concept would later appear in Resident Evil 7: Biohazard.
- 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 "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 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.
The quick time events and over-the-shoulder 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 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 Resident Evil 2, 3 and 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 Bottomless Magazines (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 Rule of Cool factor of being able to wield the iconic submachine gun was too great to cut it out entirely.
- Right before they settled in Not Spain, the game location was a village in Eastern Europe. This would later be revisited in Resident Evil Village, 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.
- Writing by the Seat of Your Pants: The game was written by Shinji Mikami in just three weeks, which likely accounts for the somewhat bizarre Denser and Wackier storyline.
Trivia / Resident Evil 4