G.U.N.

From Sonic Retro

G.U.N. (Guardian Units of Nation) is an army in the Sonic the Hedgehog universe. They were responsible for the shut down of Space Colony ARK and the death of Maria Robotnik. The army believed that Gerald Robotnik's research would be a threat to the planet, and so organized a plan to shut down ARK and destroy Project Shadow. They would invade the ARK under the ploy that there was an accident and do away with anybody that worked on Project Shadow. They then captured the Biolizard and encapsulated it. However the then-finished project, Shadow the Hedgehog, fled in an escape capsule. During the video game Sonic Adventure 2 the G.U.N. army's robots are constant enemies.

The role of GUN in Shadow the Hedgehog's' plot is to repel the invasion of Earth by the forces of the Black Arms by any means necessary - including the (presumingly unwanted) assistance from Sonic the Hedgehog and his friends. During the opening FMV sequence, it is shown that Earth is being overrun, with GUN's forces almost helpless - hence the temporary alliance. It is also strongly hinted during the game and FMV sequences that GUN's mission is the investigation (and possible destruction) of Shadow himself, depending on the player's moral choices within the game. (There attempts at doing this are mainly caused by the commander of GUN due to his personal hatred of Shadow, although in one ending he realizes Shadow isn't evil.)

GUN's role in Sonic Adventure 2 was also expanded in Shadow the Hedgehog, where a one of the levels takes Shadow and Maria through the colony during the GUN incursion and it also shows Shadow fighting one of the weapons after they harm Maria. This is the only game where GUN was not a villain. It is likely that they, like Dr. Eggman, have merely temporarily allied with Sonic for convenience.

Sonic the Hedgehog series characters
Heroes	Sonic (Super, Hyper, "Dark Super", Darkspine, the Werehog) | Tails (Super, Turbo) | Knuckles (Super, Hyper) | Amy Rose | Cream | Blaze (Burning) | G.U.N. | Silver (Super)
Anti-heroes/Neutrals	Shadow (Super) | Rouge | Chaotix | Mighty | E-102 Gamma | Chaos | E-123 Omega | Emerl | Rogues
Villains	Dr. Eggman/Dr. Ivo Robotnik | Metal Sonic | E-Series | Biolizard | Black Arms (Black Doom) | Gemerl | Fang
Other	Gerald & Maria Robotnik | Big | Chao | Tikal | E-101 Beta | Flicky | All Characters