The prototype for Jack was developed in Russia. Since it was just a step in the production, the skin was removed from the mecha. Prototype Jack (or P. Jack, for short) was built only for power, so his power capacity far surpasses that of the completed Jack. The tournament's sponsor, Heihachi Mishima, has entered P. Jack into the contest in order to pit him against Jack.
After the first King of Iron Fist Tournament, the remains of the first Prototype Jack unit (a first-stage model of the final Jack model) were repaired after almost being destroyed by Jack's rampaging combat abilities. Upon reactivation, P. Jack complained that his alter-ego had received a refit, and he repeated his complaint until his fuel ran out. Now resting in Kazuya Mishima's laboratory, P. Jack was left untouched for months before a back-up fuel supply reactivated him, and once again he began his constant pleas for a new look. To quiet him, Kazuya gave his captured scientist, Doctor Bosconovitch, the task of remodeling the robot.
With a cunning memory change, the doctor managed to convince P. Jack that his new body afforded him superior protection to Jack's, despite it being only a hat and sunglasses. Kazuya is currently goading P. Jack, demanding more programmed maneuvers in time for The King of Iron Fist Tournament 2. Having repeated his fighting moves over and over (to such an extent that the doctor disconnected P. Jack's voice box), P. Jack now feels his next encounter with Jack will have a much different conclusion.
Ending Description: Prototype Jack traverses a tunnel and emerges from the shadows into a chamber with a vertical opening. P. Jack turns on the boosters in his legs and rises upward, into the sky. As he flies away, he explodes and three screws drop back onto the ground.
In Tekken: The Motion Picture, three Prototype Jack robots are programmed to protect the labs in which Lee Chaolan and Heihachi Mishima had their test subjects hidden. There comes a point in time where the three Prototype Jacks and Jack-2, along with Lei Wulong, have a battle in the middle of the lab.
Prototype Jack appeared in Tekken Tag Tournament as a playable character.
Prototype Jack appeared in Namco X Capcom as an enemy character. He first appears in Chapter 14, along with a second Prototype Jack, as part of Waya Hime's army when she attempts to ambush Bravoman and Jin Kazama.
Prototype Jack appeared as a playable character in Tekken Tag Tournament 2, sporting the same look he received in Tekken 2 and the original Tekken Tag Tournament. His fighting style is very similar to Jack-6's, although he has a slightly different moveset.
Ending Description: A large Prototype Jack is being built, when a Prototype Jack walks toward to it and stares at it while the body of the larger robot opens and some steps descend. P. Jack enters into the stomach of the robot and sits down at a control panel, activates the robot, and prepares to launch with a countdown while the other construction Prototype Jacks leave the perimeter. Just as the giant P. Jack launches, a construction Prototype Jack rushes in carrying a large screw, desperately waving to the pilot in an attempt to get him to abort the (incomplete) giant P. Jack's launch. The pilot, however, misinterprets the worker's actions as a simple good-bye wave, and does a thumbs up. The construction Prototype Jacks are left to watch helplessly as the giant P. Jack launches, rising high into the air before exploding, after which three screws fall back into the hangar.
All Jack robots embody the huge, slow and powerful fighter archetype: they need only a few solid hits to destroy an opponent, but they're very slow and their limited moveset can get predictable, so they require good timing. Jacks deal good damage and possess good pokes and throws, but the real advantage comes from the long range of many of their attacks - most of their punishers are able to hit from afar.
In Tekken Tag Tournament 2, Prototype Jack returned with a moveset nearly identical to Jack-6's. There are some differences between the two, mainly with Prototype Jack utilizing his spinning limb related moves while Jack-6 possesses extendable arms, but their core gameplay is essentially the same.
While other characters utilize the Martial Arts, 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. Prototype Jack is no exception.
- Prototype Jack is the only Jack model who doesn't have plutonium blood (his is gasoline).
- P. Jack is also the only Jack robot that has competed in more than one tournament in the Tekken universe, despite the fact that there is a large difference between his appearance in Tekken and Tekken 2.
- Prototype Jack was destroyed by Jack-2 in the second tournament, as detailed in his Tekken 2 ending.
- Unlike the other Jack models, Prototype Jack is fitted with a rocket booster, built into his leg. P. Jack's internal support system can provide up to three "detonations" to the booster.
- His arm and body are somewhat "loose", as he can spin his hand freely without limitation.
- In Tekken Tag Tournament 2, If the player leaves Prototype Jack alone for about six seconds, he will shut down and reboot himself.
- Prototype Jack's Tekken Tag Tournament 2 ending is a re-imagining of his Tekken 2 ending.
- Prototype Jack, along with Jack-2, Gun Jack and Jack-6 are the only Jack robots to appear in more than one game.