|“||You got a mission? Don't sweat it. We'll crank it up to Jacks-imum overdrive! Jack attack!||„|
|~ Greg Jack saying the Mad Jacks' sales pitch.|
|~ The Mad Jack's catchphrase.|
The Mad Jacks are minor antagonists in Big Hero 6: The Series. They are a group of destructive and high-tech mercenaries who take on dangerous missions in an "extreme" manner.
Greg is voiced by Rob Riggle, Jack is voiced by Kevin Michael Richardson, and Jaq is voiced by Kerri Kenney.
In "The Impatient Patient", the Mad Jacks are hired to steal a hard drive that Alistair Krei purchased on the black market. The three attack Krei on his yacht as he is trying to return to the harbor with the drive, but are intercepted and foiled by Hiro and Baymax, although Hiro develops the flu as a result of their fight. Following this, the Mad Jacks are contacted by their employer, Obake, who berates them for losing to a child and orders them to finish the job. Later, Fred researches the Mad Jacks and informs Hiro, GoGo and Honey Lemon that they are a shadow ops team who not only have their own website, but theme song as well.
Meanwhile, Krei has finished doing the same research on the Mad Jacks, and, as he prepares to have the drive probed, Jack and Jaq crash into his window. Krei remarks that his windows are impenetrable, although his assistant asks if his windows are the only thing that is impenetrable, leading to Greg Jack rocketing through the floor and kidnapping Krei. While they are making off with Krei, Jack grabs Hiro as he is trying to pursue them alone and drops him into a dumpster, breaking his leg.
The Mad Jacks take Krei back to their headquarters, a mobile airship, and force him to hand over the drive before hanging him off the Krei Tech building. The Jacks then head to Obake's lair, where Greg Jacks hands him the drive. Obake then notices that Big Hero 6 is approaching and Greg Jack opts to distract the heroes while he gets away, although, since Obake prioritizes the drive's security over all else, Greg Jack decides to hold onto it instead. The Mad Jacks then engage Big Hero 6 in a fight, and, after Greg Jack takes Baymax out with a giant cannon, Hiro intervenes by using a robotic duplicate of himself and helps his friends fight the Mad Jacks off. Hiro and Baymax soon take the drive back from Greg Jack, but are unable to prevent him and the other Jacks from escaping. Ultimately, it is revealed that selling Krei the drive and hiring the Mad Jacks to "steal" it was all part of Obake's plan to trick Krei into using it without having it checked, resulting in him gaining secret access to all of Krei's files, including one revealing Hiro's secret identity, through a bug in the drive.
- It is unknown if all the Mad Jacks' real names are actually "Jack", or if they all use Jack as a codename, considering the Jacks' leader's real name is Greg, while the other Jacks go without confirmed names.