Originally human scientist Michael Gehabich, grandfather to Alice Gehabich, Hal-G was created during a dimensional transporter experiment. Michael accidentally crossed into Vestroia and encountered Naga. This event triggered Vestroia's initial collapse and caused Michael's possession by the Silent Core's negative energy, transforming him into Hal-G. His physical form drastically altered, gaining green skin, pink hair atop a balding head, elf-like ears, small horns, and a distinctive purple suit with cape. As Hal-G, he became Silent Naga's primary human agent and partner, serving as a secondary antagonist to advance Naga's plans for seizing the Infinity Core and dominating both Vestroia and Earth. Hal-G manipulated events covertly, notably commanding Masquerade (later revealed as Alice's alternate persona) to defeat Dan Kuso and the Battle Brawlers. He utilized a transporter to dispatch Naga and other minions to Earth while trapping the Battle Brawlers in Vestroia. In a pivotal deception, Hal-G feigned an internal struggle between Michael's personality and his own, tricking Alice into transporting him to Wavern at Wardington Palace. Once near Wavern, he released Naga to attack her. He engaged in multiple battles, swiftly defeating Shun Kazami, Chan Lee, and Joe Brown. His final confrontation was against the combined Battle Brawlers. During this battle, he deployed the Fifth Paladin to corner Drago, but the unified Bakugan of the Battle Brawlers overwhelmed his forces. Following Naga's destruction due to a phlebotinum overload, Hal-G was expelled from Michael's body, erasing the Hal-G persona entirely. After defeat, Michael Gehabich reverted to his original self with no memory or lingering traces of Hal-G. In subsequent events, Michael aided the Battle Brawlers by providing access to his dimensional transporter technology for travel between Earth and New Vestroia. Hal-G exclusively partnered with Silent Naga as his guardian Bakugan across all media. While the video game adaptation features a similar character, Marduk, partnered with Vladitor, Hal-G himself does not appear or participate directly in those events.