Jack (ジャック Jakku?, Russian: Джек), sometimes capitalized as JACK, is the name of a series of robots that are upgraded in each main installment in the Tekken series of fighting games. There has been a playable Jack model in every main Tekken game, except for Tekken 4. Prototype Jack is seen as separate to the main line. The first Jack was built by the Russian military, a killing machine built purely for destruction.

After proving himself in the first King of Iron Fist Tournament, updated Jack robots were put into mass production and utilized in battlegrounds. During this time, one of the Jack-2 robots came across a young girl. Suddenly developing a conscience, Jack-2 took it upon himself to look after the girl, up until the point he was destroyed by Doctor Abel. After this, Jane, the young girl rescued by Jack-2, grew up determined to restore the robot who saved her as a child. Although Jane was successful in installing Jack-2's memories into the new Gun Jack model, Gun Jack was ultimately destroyed.

After this, Jane joined the G Corporation, where she continued to work on building Jack robots in the hope of restoring her beloved companion. Starting with Jack-2, Jane transfers the memories and sentience of the latest playable Jack to the next playable model, meaning that all the playable Jacks after that have technically been the same "Jack". 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 a letter from Kazuya. The letter was 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 was unknowingly bumped into by Lucky Chloe, who happened to be outside at the same time, atop of the tower peacefully listening to music.

Unfortunately for Jack-7, the letter from Kazuya got blown away by a gust of wind, and as he jumps to catch it, he unknowingly jumps from the building and falls to the ground. After seeing Jack's fall, Lucky Chloe goes back inside the tower, unconcerned.