Jackhammers, also known simply as Jacks (not to be confused with the Jack robots), are characters exclusive to the live-action Tekken film.
They serve a similar purpose with the Tekken Force, as an army employed by the Tekken Corporation to carry out their orders. However, a big difference between the two is, whereas the Tekken Force specialize in hand-to-hand combat, Jackhammers are equipped with firearms to shoot down or detain their targets, as seen in the film's opening scene where they kill the gunmen chasing after Jin Kazama, while Jin himself just barely manages to evade them. Originally answering only to Heihachi Mishima, he turns over control of them to his son, Kazuya Mishima, while the Iron Fist tournament is being held. Kazuya would later use this to usurp Heihachi and have him executed, although a scene following the end credits ("I am Mishima Heihachi. I. Am. Tekken. You will obey.") reveals that the Jackhammer issued with this task did not go through with it. Following Jin Kazama's victory over Kazuya in the Iron Fist tournament, they fall under his command, surrounding Jin on both sides as he heads home.