David Bowie's 1974 song (and album) 'Diamond Dogs' was a musical adaption of George Orwell's famous book '1984'.
Hideo Kojima is a known David Bowie fan and in the Metal Gear Solid 5 trailer, it is stated that Big Boss has been in a coma for 9 years; 'Metal Gear Solid: Peace Walker' - which precedes the events of MGS5 - was set in November 1974, placing MGS5 in late 1983 or (more probably) 1984, the year of George Orwell's novel, with Big Boss shown to be part of a new squad known as 'Diamond Dogs', a direct reference to the album.

The demo Hideo Kojima showed at GDC 2013 for The Phantom Pain starts with the words, "Okay Ahab, time to go." A bandaged man then turns and runs to Snake, saying, "You can call me Ishmael." Snake is also revealed to have a prosthetic left arm and in the actual trailer for the game you can see a large flaming whale. These are all allusions to the novel Moby Dick. The main character in Moby Dick is named Captain Ahab, the first words in the book are "You can call me Ishmael", and Ahab has a wooden leg and is hunting the whale that took it.

There are many differences between the original "Metal Gear 2: SOLID SNAKE" on MSX and the version included in "Metal Gear Solid 2: Subsistance". In the 2006 version of "Metal Gear 2: SOLID SNAKE" they changed the portraits in the "codec calls" with Yoji Shikawa's artwork, and they also added a new line in Gray Fox's speech after you defeat him:

In Japanese
その時、俺は耳も鼻もそがれ。。。ひどい状態だった

In English:
"They had cut off my ears and my nose, I looked terrible"

These new words fit perfectly with Ishmael's bandaged face in Metal Gear Solid 5.

The watch used in the "MGS5 E3 2013 trailer" is a Seiko G757 5000. This watch is almost identicle to the watch also used by James Bond (Roger Moore) in the movie Octopussy, the Seiko G757 5020 Sports 100.

This game is named after a real medical condition. Phantom pain is pain that feels like it's coming from a body part that's no longer there. Doctors once believed this post-amputation phenomenon was a psychological problem, but experts now recognize that these real sensations originate in the spinal cord and brain.

Kiefer Sutherland was recommended to Kojima for the role of Snake by Avi Arad, who is producing the Metal Gear Solid movie.

It was originally intended for both parts of Metal Gear Solid V, Ground Zeroes and The Phantom Pain, to be a single game, but the game's designer, Hideo Kojima, wanted people to experience the game near the launch of the recently announced next generation of consoles (PlayStation 4 and Xbox One). Ground Zeroes was also considered for the PlayStation Portable, but development proved to be much tougher than expected, and that version was cancelled.

However, in 2023, Kojima stated on Twitter that he originally intended for Ground Zeroes to not just be released separately as a prologue to The Phantom Pain all along, but he also intended it to be the first installment of an episodic series. His reasoning for this was due to lengthy development times for recent games resulting in ideas changing over the course of production. His original plan was to produce the first episode to gauge audience reactions, and then develop two more episodes while receiving feedback, but due to criticism over the game's short length and pricing, and subsequent confusion over whether or not Ground Zeroes was considered a full game, this plan was scrapped.

In a hut in the Angola-Zaire Border Region, a radio can be found which if you listen to it plays the radio news broadcast from the Silent Hills demo P.T.

The codename of the Aerial Command Center, pequod, is named after the ship belonging to the whaling crew featured in Moby Dick.

The game's PC retail release is simply a CD with nothing but a Steam installer file on it, making the contents take up a total of only 8.78mb and contain no data actually retaining to the game itself.

This was widely considered a grievous decision, as many players who purchased the retail copy of the game likely had unstable or restricted bandwidth on their internet connection, making the 28GB download a struggle.

There was originally a final mission planned that was ultimately cut from the game, called Spoiler:Mission 51: Kingdom of the Flies. The mission would have tied the final loose-end of Eli running away with Sahelanthropus alongside the war-children and the remaining English vocal-cord parasite. A new area, an island surrounded by a salt lake located in Central Africa, was planned for the mission as well.
XOF Soldiers and Child Soldiers would be patrolling across the island until Snake finally confronts Eli inside of Sahelanthropus, resulting in a final fight that would end with Sahelanthropus being destroyed. It is revealed that Eli intentionally infected himself with the English vocal-cord parasite that the Floating-Boy gave him, and he is left behind to either take his own life or to die to incoming Napalm strikes on the island. After Snake and Diamond Dogs leave the island, the Floating Boy uses his powers to remove the parasites and takes him off the island.
Only 30% of the cutscenes were ever finished, and footage shows no facial animations on any of the characters. It is unknown how much of the island itself, or the boss fight, were ever completed.

The game originally had an "80's filter" during production. According to director Hideo Kojima, it was inspired by the 2013 film Rush, which itself "had very 70's texture & tone of film." As the game's story was set in 1984, the team studied and developed a filter reminiscent of the 1980's. However, once it was used in fullscreen, it ultimately demanded too much processing power, slowing the game down significantly. This ultimately caused the feature to be removed in the final product.

The Battle Gear was originally planned to be used on the actual field, as opposed to just Combat Deployment missions. According to director Hideo Kojima, the Battle Gear "disrupted the gameplay balance during test sessions", which eventually lead to its actual use being removed from the final product.

If the player does a punch attack while sprinting, the classic "bionic strain" sound effect from the 1974 television series The Six Million Dollar Man will play. Venom Snake himself also has a bionic arm to help further cement the reference.

Spoiler:After the release of Patch 1.06, it is possible to recruit Quiet once again after she leaves Mother Base in "Mission 45: A Quiet Exit". By replaying "Mission 11: Cloaked in Silence" several times, the mission will be renamed "Mission 11: [Reunion] Cloaked in Silence". Beating the mission this time will have Quiet once again available as a buddy.

Spoiler:The Third Child's appearance changes depending on who he's being emotionally influenced by.

- He'll have shrapnel in his head when controlled by Venom Snake.
- His sleeves will be on fire when controlled by The Man On Fire.
- His mask will change to resemble Skull Face's mask when controlled by him.
- He'll be wearing Shabani's necklace when controlled by him.
- He'll have Eli's red cloth on his shoulder when controlled by him.

During "Mission 2 - Diamond Dogs" on Mother Base, it is possible to shoot Ocelot with a tranquilizer gun. Doing so will make him say a few comments instead of knocking him out. Sometimes he will say "La Li Lu Le Lo", in reference to the Patriots from Metal Gear Solid 2: Sons of Liberty.
He will also sometimes say "Kawanishi-Noseguchi, Kinunobebashi, Takiyama, Uguisunomori, Tsuzumigataki", which is a shortened list of the names of train stations of the Myōken Line, operated by Nose Electric Railway in the Kansai region of Honshū, Japan. This is also a recurring easter egg that started in the first Metal Gear Solid.

During mission 29, Spoiler:if the player shoots down the chopper that arrives after defeating the skulls, instead of the usual "Game Over" text it will change to "Time Paradox".

The same thing can happen on the first mission in the game. Spoiler:If it takes more than three days to rescue Kaz the cut-scene will be different, and the text will again change to "Time Paradox".

In 2020, Konami in collaboration with prosthetics company Open Bionic released an official Metal Gear Solid "Venom Snake" Cover, based on Venom Snake's prosthetic arm in the game, for use with Open Bionics' "Hero Arm" prosthetic. The "Hero Arm" can be used by any upper arm amputee below the elbow. Daniel Melville from the town of Reading in the United Kingdom was the first to receive the design, an avid gamer and fan of the Metal Gear series.

Big Boss' final vision of Paz in censored the Japanese version of the game. The scene is altered by using different camera angles and animations of Paz to obscure gore. In a later update for PC, this scene was also censored worldwide.