Resident Evil 4 was in production for many years due to the constant changes it went through. The game was scrapped and started again four times. One of the scrapped versions though eventually became its own franchise titled Devil May Cry.
The earliest version of the game was announced for the PlayStation 2 under Resident Evil 2 (1998) (Resident Evil 2) director Hideki Kamiya. This build was eventually cancelled as a Resident Evil installment and became the title known as Devil May Cry (2001). Eventually, development was moved to the GameCube console and another build emerged. This was the first version to feature Leon from RE2. The first version shown had Leon sporting a variation of his current costume and fighting a mist-like virus. The second shown version's showed one bad guy in particular that sported a hook on one of its hands, and the logo for the game reflected this (this can still be seen in the final logo). One more version was created and cancelled before Shinji Mikami took over and transformed the title into what it is today. Of all the builds developed, only one of them was never unveiled to the public (it was the one that was being worked on right before Mikami took over). In Japan, an exclusive DVD bonus disc included with the game has footage from the second version that was made.
The hallway sequence where the player has to dodge lasers via quick time events, is likely a reference to the 2002 Resident Evil movie where the film's characters encounter almost the exact same situation.
This is the first Resident Evil presented in 16:9 widescreen. All previous entries were displayed in 4:3 fullscreen. This is why when the game is played on an 4:3 television it appears to be letterboxed.
The original GameCube version contains a unique glitch where sometimes after reopening a save file, Leon will move sideways instead of forward. If you reset the game and reopen the save file though, Leon will walk straight again.
Resident Evil 4 was originally part of an exclusivity deal between Capcom and Nintendo. As a ploy to attract older gamers with more mature games Nintendo had Capcom develop three Resident Evil titles exclusively for the GameCube. These three games were Resident Evil (2002), Resident Evil 0, and Resident Evil 4. Due to Resident Evil 4's immense popularity though Capcom decided to make it multiplatform by porting it to the PlayStation 2 and PC. In order to do this Capcom and Nintendo altered their deal to where Capcom would port Resident Evil 2 and 3 exclusively to the GameCube for the remainder of the 6th console generation. Resident Evil 4 has since been ported to the Wii, and has been remastered for the Xbox 360 and PlayStation 3. It was then updated again for a PC re-release which later became the basis for ports to the Xbox One and PlayStation 4.
An Xbox One and PlayStation 4 remaster of Resident Evil 4 was announced on February 25th, 2016, and was released on August 30th of the same year. This remaster ended up just being a port of the PC's Ultimate HD Edition to consoles. The PlayStation 4 and Xbox One versions render in 1080p at 60 frames per second, features the updated textures and character models from the PC's Ultimate HD Edition, and include all bonus content from all previous versions of the game. There is no option to use the original GameCube assets though, unlike the PC's Ultimate HD Edition.