In the videogame series, Tekken, the Devil Gene is a mysterious curse that befalls anyone born of the Mishima bloodline.

Before Tekken 5, it was believed that the curse began with Kazuya, who sold his soul to the Devil in order to exact revenge on his father Heihachi, who had thrown him into a ravine when he was a child. However, due to the introduction of Jinpachi Mishima in Tekken 5, and some of the dialogue found within the game's story mode, it's clear that the Devil Gene predates this. Speculation states that Jinpachi may be the originator of the curse, but there won't be any way to know for certain until answers are given in subsequent games or by Namco themselves.

One thing to note about the Devil Gene is that Heihachi lacks it. It's not known why this is, except for the theory that Heihachi simply doesn't want it. However, this does not answer why it affects Jin Kazama, who also rejects it. However, Heihachi does have a use for the Devil Gene. With samples taken from Ogre's tissue, he has learned that combining the Devil Gene with Ogre's DNA will allow him to finally create the ultimate lifeform he seeks. The connections between the Devil and Ogre are as of yet unknown.

Another speculation made about the Devil Gene is that the individual Devils are independent of each other, and yet part of the same whole. In Tekken 4, Kazuya's Devil refers to the one within Jin as his "other half" that he wishes to absorb into himself again. However, if each successive Devil is subtracted from the one before it, that would mean that Jinpachi's is only half of its original self while Kazuya's is only 1/4th of Jinpachi's original, and Jin's is another 1/4th. of the original Devil. If Heihachi possesses a Devil Gene, but merely supresses it, then these numbers are further multiplied by 1/2.

While complicated, this would explain why each Devil looks quite different than those before it. Jinpachi's Devil is purplish with horrible skin disfiguration and a gigantic mouth in its abdomen. Kazuya's Devil retains the purple color and adds horns, leathery wings, a tail and a third-eye, but lacks the more severe skin disfiguration and the gigantic mouth. Furthermore, Jin's Devil lacks the purple color, tail, and the third-eye, but retains the wings (albeit in black, feathery form) and horns while adding black tattoos across his body. In addition, in Devil Jin's ending, he absorbs Jinpachi's Devil and gains the purple color and third-eye along with a few other unique features.