- RTM dub name: Sappo
Jack was one of a group of diminutive refugee Autobots that left Cybertron four million years ago, along with his friends Chromedome and Abel. Eventually, they crashed on the inhospitable world of Master, but were eventually able to establish a civilisation through numerous technological advancements. One such advancement was the development of Headmaster Transtectors, which required the young Autobots to undergo extensive training to master the transformation skills necessary to become a Headmaster. Jack, unfortunately, lack the necessary physical skills and washed out of the program, but he put his mind to use in helping to develop Fortress's massive Transtector, Battleship Maximus, and it's weapon, the Master Sword.
When the Decepticons invaded planet Master in the year 2011, Jack was among those who attempted to fight back. Manning an artillery emplacement during a battle, Jack refused to abandoned his post even when the fight seemed hopeless, but the tide turned when Chromedome and the other Autobot Headmasters arrived to save the day. Jack still bore a misplaced grudge against Chromedome for successfully becoming a Headmaster where he could not, and would not talk to his old friend at first, but after collapsing and being taken to Battleship Maximus for medical treatment, he was forced to confront his feelings. Chromedome helped him to realise that just because he was a Headmaster, he was no better than Jack was, and that Jack's intelligence made him just as great an asset as any power Chromedome possessed. Unfortunately, this happy reunion was shattered by the Decepticon ninja Sixshot, who impersonated Chromedome long enough to get close to Jack and capture him, taking him back to Scorponok and torturing him for information on the Master Sword. When Jack proved unable to provide the secrets Scorponok wanted, Sixshot cut his losses and decided to send the 'bot on a suicide mission instead. He planted a bomb within his chest and weapons systems in his hands, and had Mindwipe hypnotise him into walking into Battleship Maximus, where the bomb would explode, destroying the craft. Jack was sent on his mission, but Twincast detected the bomb within him, and Chromedome was forced to kill his friend to stop him. With his last words, Jack apologised to Chromedome, and was then consumed by the explosion. Sixshot had now taken both Abel and Jack from Chromedome, and he vowed vengeance against the ninja.