Guardian Units of the Nations (Sonic X)

The Guardian Units of the Nations, also known as GUN, is an organisation in Sonic X. It is a military organisation that is affiliated with the President armed with their expertise in warfare in order to protect humanity and maintain peace in Earth.

Early life
Around 50 years prior to the events of Sonic X, GUN was called to deploy troops to Space Colony ARK in order to stop Project Shadow, a research project led by Professor Gerald Robotnik that aims to create the "Ultimate Lifeform" because the government deemed it as a threat. They have killed most of the researchers (except for Gerald) and stopped their research projects, sealing the prototype of the Ultimate Lifeform away in the ARK. Maria, who attempted to release the completed Ultimate Lifeform (Shadow) was also killed. GUN would later have shut down the ARK for the next 50 years.

New World Saga
Following the arrival of Sonic the Hedgehog, his friends and Dr. Eggman, GUN grew suspicious of the new inhabitants and in particular, Dr. Eggman, for his world domination schemes.