Colonel Zachary Arnold is a member of the United Earth Federation and an EarthCom veteran. A weathered man in his late 40s, Colonel Zachary Arnold has spent the better part of his life in the blue of the UEF. Though he is well past the maximum age for field service, Arnold has used his extensive connections to stay in combat. Because he has few true friends and his wife died of cancer many years earlier, Arnold prefers to stay on the frontlines, waging his own style of warfare against the UEF's enemies.
Arnold has been at the forefront of so many battles that both the Aeon and Cybrans have extensive files on him. It is even rumored that all Aeon Commanders-in-Training are required to attend a special seminar on his favored tactics.
Arnold was rumored killed during "Operation Metal Shark" when his ACU was destroyed by an overwhelming Aeon assault force. He is however later revealed still alive, transformed into a knight of the Aeon Illuminate. General Samantha Clarke, surprised by Arnold's transmission, labels him as "brainwashed" by the Aeon. Arnold then leads an Aeon assault on Black Sun in "Operation Stone Wall."
Arnold will die at the end of each campaign, no matter which one is selected.
- If playing as the UEF, Arnold will lead an assault against the player in the final operation of the game. When Black Sun is charging, he directly assaults the position with his army, and is killed by the player.
- If playing as Cybran, he is killed when the UEF forces nuke his island base. He also attacks black sun.
- If playing as Aeon, Arnold is an ally in the last mission, but never seen in combat. After the Cybran commander RedFog is defeated, he claims his true allegiance to the Princess. Marxon, who was working with Arnold at the time is enraged by this, and kills Arnold by self-destructing his ACU. Marxon is promptly killed by the player.