The original Jack is a super slaughtering military machine and super killing robot developed by the former Soviet Union. The Russian military got wind of Kazuya's world coup d'etat plans right away and sent Jack to the tournament to get rid of him. Only a robot could boast such violent attacks and stupendous power.
In his ending, Jack is strapped onto a machine. More Jacks are shown being activated. The scene ends with metal doors closing, which say "Danger".
The original Jack is the rival of Prototype Jack.
Jack-2 (Tekken 2)
Jack-2 was an upgrade of Jack, who appeared in the original Tekken game. Jack-2 makes his only canonical appearance in Tekken 2. He is also in Tekken Tag Tournament, but this game is non-canonical. Jack-2, like the original Jack, was also a rival of Prototype Jack. He was destroyed by Doctor Abel, which is shown in Jack-2's Tekken 2 ending.
Gun Jack (Tekken 3)
Jane, still haunted by memories of Jack-2's fate nineteen years later, works on a way to restore Jack-2. She learns that most of the technology responsible for Jack-2's A.I. was created by Mishima Heavy Industries, a subsidiary of the Mishima Zaibatsu. She also finds the ground work for something called "Project Gun Jack", an upgraded Jack with the addition of a pivot gun. Jane snuck into Mishima Heavy Industries and secretly installed the hidden program. Dr. Abel tried to destroy this version of Jack by firing an electromagnetic burst from a satellite, but he ultimately failed due to Gun Jack's energy shield protecting himself and Jane.
At the third tournament's conclusion, Heihachi Mishima's Tekken Force attacked Jane. She was rescued by Gun Jack, who was destroyed by the onslaught of gunfire. Jane escaped with the help of G Corporation.
This version was mass-produced and sent to attack Heihachi and Kazuya Mishima at Hon-Maru. Apparently, this model has a self-destruct feature, as shown in the Tekken 5 opening movie, where a Jack-4's head opens up to reveal an internal time bomb. The massive explosion wasn't enough to kill Heihachi, but the blast did however throw him several miles as well as free Jinpachi Mishima from his imprisonment.
Several Jack-4's also appear in the Scenario Campaign Mode of Tekken 6, fighting for the G Corporation.
Despite Jack-4 only appearing in Tekken 5, it's considered the Tekken 4-era Jack, since it first appears in the game's opening, set during the fourth tournament, and it's numbered "4". Jack-4 fills the lack of any Jack in Tekken 4, making later Jacks' number match the game's.
Jack-5 (Tekken 5)
Jack-5 was created by Jane as an upgrade of Jack-4 and used the fifth tournament as a means of testing Jack-5. Returning to have his emotion program installed, Jane downloads Gun Jack's memories into him, but the results cause him to go berserk, ripping free and trashing the lab. As he brings down his arms in a crushing blow on Jane, the memories re-assert themselves and Jack-5 stops, looking over his body in confusion. Jane goes to him and he picks her up in his arms gently, his original personality fully restored.
Jane successfully restored Jack-5's memory at the completion of the 5th King of Iron Fist Tournament. It was not long until the Mishima Zaibatsu decided to make their own Jack model, which has been built with 10 times the power of Jack-5. The new G Corporation leader Kazuya Mishima also demanded a new Jack model eventually creating Jack-6. They decided to test Jack-6 in the King of Iron Fist Tournament 6 to destroy the Mishima Zaibatsu.
In Tekken 7 Story Mode, an army of Jack-6, being sent by Kazuya, interrupts the battle between Akuma and Heihachi at the Mishima dojo, who temporarily joined forces to defeat the onslaught of Jack-6 robots.
Jack-7 (Tekken 7)
It was no secret that G Corporation was locked in a power struggle with the Mishima Zaibatsu. However, within G Corp itself, another battle was raging: the battle to create the ultimate next-gen humanoid weapon.
On one side was the development team behind the Jack series led by Jane; on the other was the research team responsible for Gigas, a bio-enhanced super human. With his massive size and uncanny mobility, Gigas was hailed for his versatility in combat, and some saw him as more than capable of dislodging the Jack series from its position as G Corp's premier weapon.
Both teams entered their weapons into the King of Iron Fist Tournament to decide once and for all which was the best, and Jack's opponent was a wrestler in a jaguar mask.
Ending Description: After defeating King in the tournament, Jack-7 is seen back at the G-Corporation Tower reading the letter from Kazuya. The letter was a proof of recognition of Jack as the chief humanoid weapon in G Corporation, with that they received unlimited funding to further the program, and 25$ monthly allowance for personal use. The letter got Jack-7 excited and during his victory dance, Jack-7 is unknowingly bumped into by Lucky Chloe, who happens to go outside at the same top of the tower, peacefully listening to music. Unfortunately, the letter from Kazuya got blown away by a wind as Jack-7 tries to catch it. Jack-7 managed to catch the letter, he however had unknowingly jumped away from the building and fell to the ground. After seeing Jack's fall, Lucky Chloe goes back inside the tower, unconcerned.
As mentioned above, both Jack-2 and Gun Jack appeared playable in Tekken Tag Tournament.
There is a playable Jack model called Jack-X (Jack Cross) exclusive to the game. This Jack model is based on Jack-6 and is told to be its backup model. Its partner is Bryan Fury. Guile's Swap Costume is based on Jack-X's design.
Jack-6 appears playable in Tekken Tag Tournament 2.
Jack-6 appears in Tekken Revolution as a playable character.
Modified Gun Jack
In Tekken 5, several Jacks appear in Devil Within mode as generic minions. Their attacks are similar to Hwoarang's moveset.
All Jack robots embodies the huge, slow and powerful fighter archetype: they need a few solid hits to destroy an opponent, but they're very slow and their limited moveset can get predictable, so they require a good timing. Jacks have good damage, good pokes, and good throws, but the real thing that makes them shine is their ridiculous range on most of their moves. Most of their punishers hits from very far away.
Jack-6's arms can be extended with some charged moves, allowing him to increase his (already long) range.
The giant robotic upper body gives the Jack robots formidable swiping range, strong physical clout, and some very useful lows. The myriad of commands throws are noticeably more damaging than the norm and throughout the series the Jack robots remained one of the strongest, if not the strongest, single throw fighters in Tekken.
Despite a move set that lacks any hint of evasiveness and more than a few clunky slow commands, The robots has an impressive mix of attacks that balance out the sluggishness. With an arsenal of trusty, solid mids and some lows ranging from pesky to lethal, an advanced Jack will use good movement and attack mix ups to be a nightmare at middle distances. It's close range game is slower and riskier but includes the threat of command grabs that will annihilate anyone incapable of breaking throws.
While other characters do fight, what Jack robots do is best described as "using brute force to annihilate the opponent", and their fighting style is listed as "Brute Force" accordingly.
- Jack-4 and onward developed by Jane.
- Attacked Kazuya and Heihachi Mishima at Hon-Maru.
- Attacked Raven, possibly in an attempt to discard the only eyewitness.
- The explosion caused by the Jack-4s freed and resurrected Jinpachi Mishima.
- The explosion caused by the Jack-4s was thought to have killed Heihachi Mishima, but Heihachi managed to survive.
- Tekken 4 is the only main game that does not feature a playable Jack robot.
- Gun Jack has an unlockable third outfit. After playing as him ten times, selecting him with either the triangle or start button will give him the appearance of Jack-2.
- Jack-6 can be customized to resemble Jack-1 through 5, Prototype Jack and Gun Jack.
- Jack-6 is one of the few characters who are capable of prohibiting wallsplats. That move is called Patriot Fist and the command is u+1+2.
- Jack bears a resemblance to Android 16, a character from the Dragon Ball series.
- Jack-X is the only Jack model so far that has the ability to speak, unlike the other Jacks that only make sounds and grunts (excluding Jack-2 in Tekken: The Motion Picture).
- Jack-6 and Jack-X's models remained the same as Jack-5.
- Jack-7's model is a palette swap of Jack-5, Jack-6, and Jack-X's models, being a redhead with glowing green "gaps" on his robotic body, wearing Jack-5's outfit in Dark Resurrection colors (a black torso with yellow camouflage pants).
- Additionally, as mentioned in King's character episode ending, Jack-7 can use mimicry in the same way as the dummies Mokujin and Combot.
- In Tekken: Blood Vengeance, Jack-6's dossier is briefly seen when Anna Williams opens a file containing dossiers of various persons of interest (this shouldn't have occurred though, as G Corporation was the very company that actually created Jack-6).