Fake Jack Atlas is a Duelbot disguised as a psychotic Jack Atlas. Its main goal is to give Jack a bad name so that he gets arrested and it paves the way for the rest of Jakob, Lester, and Primo's plan.
Fake Jack and his Duel Runner look similar in appearance to Jack and Phoenix Whirlwind. The only differences are that his Duel Runner and appearance (both clothes and physical appearance) have a much darker color scheme than that of the real Jack and Phoenix Whirlwind and that his eyes are red instead of violet.
It is later revealed that it was the work of an impostor and Jack rushes to find them. When he locates the impostor, "Enemy" Jack tries to run him off the road, before challenging him to a Turbo Duel.
As the duel is about to commence, an Infinity symbol appears, with Jack wondering what is causing the light surrounding them.
During the duel, the impostor constantly taunted Jack, by repetitively referring to himself as "King", much to Jack's shock and disgust. When Jack draws "Trust Guardian", he chooses to use "Dread Dragon" instead because he believed "Trust Guardian" won't fit his style of Dueling. This however allows the impostor to defeat Jack easily and run Jack off the highway and into the sea, using the real damage caused by "Red Dragon Archfiend".
Yusei and Crow arrive on the scene and the imposter distracts them with "Red Dragon Archfiend" to escape. Yusei and Crow believe Jack has gone mad.
The impostor was later pursued by Kaz, Yusei and Crow and rammed their Duel Runners while taunting at them just before the real Jack Atlas reappears for a rematch.
This time, Jack decides to use "Trust Guardian" for this Duel, knowing that his pride was what caused him to lose in their previous Duel. This allows the real Jack to turn beginning of the duel in his favor, as he is able to not only destroy the robot's copy of "Red Dragon Archfiend", but also inflict major damage to its Life Points. However, the impostor makes a comeback in trying to winning the duel by summoning 2 more copies of "Red Dragon Archfiend" and reviving the copy that Jack destroyed.
Both copies, along with the third one he had Special Summoned from the Graveyard, are able to decrease Jack's Life Points dramatically. The impostor tells Jack that he won't be able to win, given that he's not the same man as before.
However, Jack disproves this with the power of his friends and the Crimson Dragon. He summons "Majestic Red Dragon" and uses it to win the Duel. At the end, the overwhelming attack destroys the robot and its Deck completely (In the English version only his helmet, Deck, and Duel Runner are shown destroyed/disintegrated and the robot is seemingly vaporized by the explosion).
He was later seen in a flashback after Team 5D's defeated Team Unicorn and had a party where the group remembered the times that they dueled strange opponents who inflicted real damage.
In Yu-Gi-Oh! 5D's World Championship 2011: Over the Nexus, Fake Jack appears and challenges the player near the end of chapter 6, after the player's team decides to test their new Duel Runner program on the Combat Lane. After completing the game, the player can perform a sidequest where Mina enlists Misaki's help in repairing the fake Jack to act as her surrogate boyfriend. Once this sidequest is complete, Fake Jack can be dueled at any time.
Fake Jack Atlas uses the same Deck as the real Jack. The only differences are that he possesses 3 copies of "Red Dragon Archfiend" instead of 1, each with a different color scheme (purple, yellow and teal) rather than the usual red one, and that in Fake Jack Atlas's deck he doesn't have cards he acquired after episode 83, such as Red Nova Dragon. His Deck was apparently a copy of Jack's whilst he was the King created by Lester.