Gray Fox first appears in the original Metal Gear (spelled "Grey Fox" in the MSX2 version). The player's initial objective is to rescue him and obtain Intel on Metal Gear from him. Fox's sprite in the MSX2 version was a recolor of the regular prisoner of war sprite (wearing a blue jumpsuit instead of a brown one), or in the case of the Nintendo Entertainment System version, the same as the prisoner of war sprite (as the game's characters were monochrome). In addition, Fox's role is very minor, as he only gives Snake the details of the TX-55 Metal Gear and suggests that he find Dr. Madnar before disappearing altogether. Future installments added some more detail to the meeting, revealing that Fox also showed a green Snake "the ropes."
In the Previous Operations section of Metal Gear Solid, Fox's mission is erroneously referred to as "Operation Intrude N313" instead of "Operation Intrude N312."
Fox returns in Metal Gear 2, where he confronts Snake as an enemy on several occasions, while secretly assisting him as an anonymous informant. Fox's past is fleshed out in this game and his civilian identity is revealed to be Frank Jaeger ("Frank Yeager" in the MSX2 version).
Fox is the most recurring boss character in the series, being fought in a total of five boss fights throughout the games (Vamp, Liquid Snake and Revolver Ocelot are fought four times, respectively throughout the series).
Fox's portrait was modeled after actor Tom Berenger. In the re-released versions, he was redesigned to resemble his later depiction in Metal Gear Solid. Portions of Fox's character, namely his first name of Frank, as well as his attempting to elope with a Czech figure skater, were influenced by the novel Crossfire.
It is stated in Metal Gear 2, and again in Metal Gear Solid, that the hand-to-hand battle between Snake and Fox takes place on a minefield. However, Fox is able to move around freely during the fight and can only be defeated by the player. Also, while Fox does "explode" after his defeat and "final conversation" with Snake, this is the case for nearly all the bosses in the game, except Dr. Madnar.
Events before Metal Gear
Born to a German-American Father and a Vietnamese mother, his parents died during the early stages of the Vietnam War leaving him as an orphan who got discriminated a lot due to his heritage which Big Boss would eventually take in. Big Boss would later spend years training the boy to become a super soldier, honing his battle skills until he became an agent of pure destruction without any emotions. In 1966 he served in a guerrilla group in Mozambique as a child. He gained notoriety as the infamous child soldier Frank Jaeger because of his particularly deceptive exploits. He single handed killed dozens of soldiers with nothing but one knife. Blindsiding the enemy with the "innocent frankness of a young boy" then attacking with the "cold cruelty of a hunter" he gained the name Frank Hunter. The little German he spoke resulted in him becoming known as "Frank Jaeger."
Later he would be taken in by the CIA and inducted into the Perfect Soldier program. The program was so successful that Jaeger became a professional mercenary in his teenage years. Being the only surviving subject of the test he was given the nickname 'Null'. During his teenage years he was a ninja in the group FOX during the San Hieronym Takeover. This is where he betrayed Big Boss by having to capture him during a mission with the Fox unit. Though he was never able to defeat him.
Null eventually escaped the mission with a help of Ocelot. As they escaped the mission both soldiers had to kill many officers on the way Grey Fox ran into Big Boss again which led into a second battle that made Null strive to defeat Big Boss no matter what. Big Boss defeated Null yet again and took him to a hospital to seek some mental help.
Years later Frank killed two people in Rhodesia during the civil war who happened to be the parents of Naomi Hunter. Grey Fox was originally going to kill the girl along with her parents but decided to keep her. Raising her as his own little sister. In 1988 Big Boss flew Frank and Naomi to the United States and eventually returned to Africa to fight a war. In this year during an Winter Olympics Games Frank fell in love with an ice skater named Gustava Heffner who he planned on marrying but wasn't allowed to due to immigration rules.
In 1990 is where Frank became the only FOXHOUND member to receive the title 'Fox'. He was also considered to be an unofficial leader to those close to him in the group.
In 1995, Grey Fox was hired to collect data and information on the top nuclear weapon that was being hidden in Outer Heaven's base. He was able to sneak in the first fortress by using stealth where he stumbled on plans for the project. Gray Fox got caught and got held hostage in a cell but his final message to FOXHOUND was 'Metal Gear'. A beautiful friendship begins as a rookie named Solid Snake saves Grey Fox out of the cell. This friendship plays a major role throughout the series. Together the duo defeated Metal Gear thinking that was it but little do they know they were wrong. Towards the end of the battle it's revealed Big Boss was the commander of Outer Heaven and set this all up as a trap. Snake killed Big Boss who happened to be his father. Thus the adventures at Zanzibar Land begins...
In 1999 Roy Campbell became the leader of FOXHOUND and Snake was pulled out from retirement due to Zanzibar kidnapping Dr. Kio Marv and due to Grey Fox sneaking in nuclear disposal sites. Fox began transmitting Snake helpful messages throughout Codec calls under the name "Snake's #1 fan" to help him overcome obstacles and to reach his goal. Snake and Grey Fox meet face to face again where the bridge leading to where the Doctor was captivated was destroyed by Fox himself. Fox trapped Snake forcing him to fight against one another. Fox was pronounced dead due to an explosion caused by Metal Gear D... little did everyone know Fox survived as his body was placed inside an exoskeleton.
Shadow Moses Incident
"Conflict is in our blood. We can't deny it. I was born on the battlefield... And I'll die on the battlefield. All I can do is fight, Snake... all I can do is fight."
―Gray Fox to Solid Snake
In 2005, Fox decides to make his status as being alive well known as he goes out looking for his old war buddy Snake. Snake was on a mission to take down a new Metal Gear machine that Liquid Snake is after for. While being cloaked Fox killed many soldiers on the island leading to a trail of blood which Snake followed. This led to Snake unaware that it's Grey Fox under the skeleton to fit him in Hal Emmerich's lab. As Hal is hiding in the lab's closet Snake and Grey Fox can have either a sword or fist fight depending on which option the player chooses.
After the fight Snake slowly realized it was Frank Jaeger as Grey Fox left hints about the past. One of the people helping Solid Snake along the way was Naomi Hunter, Frank's adoptive sister. Frank eventually told Snake the truth about how he killed Naomi's parents and took her in as a sibling. Towards the end of the game Frank decides to help out his old friend by helping destroy Metal Gear REX. During the battle Fox lost his left arm to REX's laser canon. He was then struck against the wall by REX's beak, critically injuring the already wounded cyborg. After being subject to a stomp from the 550 ton goliath the exoskeleton Fox equipped eventually gave way and Frank Jaeger was killed. His dying words to Snake were:
"We're not tools of the government or anyone else. Fighting was the only thing... the only thing I was good at, but... at least I always fought for what I believed in. Snake... farewell..."