The Guardian Units of Nations, also known as the Guardian Units of the Nations and abbreviated as G.U.N., is a group that appears in the Sonic the Hedgehog series. It is an international military and security organization on Earth, as well as the national defense forces of the United Federation. Run by Commander-in-Chief Abraham Tower, G.U.N. has engaged in multiple incidents where it would protect Earth from all sorts of threats, including the Eggman Empire and the Black Arms. Founded over fifty years ago, G.U.N. has had a key role in several crises in recent history, including the shutdown of Project Shadow, the Space Colony ARK incident, the Black Arms' invasion of the planet, and many others. However, during the War to Take Back the Planet, G.U.N. was "put in their place" and dismantled by the Eggman Empire, leaving the organization's status after the war unknown.

The Biolizard is a character that appears in the Sonic the Hedgehog series. He was the first prototype of the "Ultimate Life Form" created by Gerald Robotnik during Project Shadow, modeled after a salamander, but was far too dangerous and flawed. After the final version of the Ultimate Life Form, Shadow the Hedgehog was created, and the Biolizard was encapsulated by the Guardian Units of Nations. Fifty years later, the creature resurfaced and tried to destroy the Earth but was ultimately defeated by the combined efforts of Sonic the Hedgehog and his friends. The Biolizard is a very large creature, being 85 meters (280 feet) long, 30 meters (100 feet) wide, and 19.5 meters (64 feet) at the tallest point on its back. It mostly resembles a grotesque, four-legged lizard with flame skin and a dark gray underbelly and possesses a long neck and medium-long and thick tail. It had three large and sharp toes on each foot which were black and had robotic parts at the joints, gill-like flaps on his sides, and possessed a large mouth with no teeth and four yellow spikes on the lower jaw. On his neck, back, hinder quarters and tail, the Bio Lizard also had yellow patches of skin. The Biolizard had several robotic parts attached to its body. Its eyes were like gun turrets, and it had a large disk-shaped machinery with a red orb in the middle on its back. The Biolizard also had several cables on its back and a set of green cables on its jaw joints, which connected with the machinery on its back, along with a stump of green cable on its forehead.