Brig. General Fletcher, a UEF commander that appears in the first mission, Operation: Black Day, was apparently an effective but somewhat paranoid soldier. He showed up in several of the following missions, although it seems he had a knack for digging against his enemies too deeply, requiring a rescue in the Fort Clarke operation, defending in Operation: Mind Games, and defeating after he went renegade and attacked Crusader Rhiza in Operation: Overlord.
A xenophobe, Fletcher was unable to accept the idea of a permanent trilateral alliance. He attacked Crusader Rhiza in Operation: Overlord and had to be terminated. Before his destruction, he announced his plans to reactivate Black Sun and kill all the Cybrans and Aeon with it. After his destruction, the mission continued, leading up to the destruction of the Quantum Arch.
Fletcher seems to suffer from some form of posttraumatic stress disorder.
When the infinite war was still ongoing, Fletcher was probably indoctrinated into believing his enemies were no less than inhuman monsters, due to the totalitarian nature of the UEF regime. As a result, he has taken very badly the fact that Cybrans and Aeons are now his allies. Fletcher took this as a betrayal of the old UEF policies, and held Hall personally responsible for this change of direction. And as a result, he seems to have gradually lost touch from reality to a certain degree, as highlighted when he said that he'll use the Black Sun to exterminate the Cybrans and the Aeons, when in fact the Black Sun was destroyed long ago.
Additionally Fletcher seems to suffer from narcissistic personality disorder. Fletcher sees himself as some sort of savior of the UEF nation. He said that he would reactivate the Black Sun by himself, and that he would resume the conflict with the Aeons and Cybrans. He hopes to rebuild the UEF to its former self yet again, with the help of some sort popular movement initiated by him and some other UEF members. Fletcher doesn't want to do this alone, and this is why he tries to "convince" the player throughout the game to share his views. This seems to hint that Fletcher is probably far from alone, and that his views are shared by many on UEF territories, due to centuries of warfare, and deep seated bigotry. Fletcher seems to represent the "dark" side of the UEF, just like Marxon was the more violent version of the Aeons. Hinting to the fact that all factions have many sides.
In Supreme Commander: Forged Alliance, the game storyline suggests that the UEF won the Infinite War by firing Black Sun and wiping out life on key planets, forcing the other two nations to submit to the UEF, eventually coaxing them into a trilateral alliance for galactic peace. Fletcher decided to attack his Aeon compatriot, thus leading to his base and commander destroyed with him inside. Fletcher was known after death as a traitor to the Coalition and total xenophobe.
If the player goes as UEF, Fletcher will sometimes secretly call him to say that he "Has a bad feeling" about the current mission, that the commander should watch his back when dealing with Aeon or Cybrans.
For obvious reasons, he is friendly, polite and relieved when he meets the player as UEF, while he is "keeping his eyes on him" if the player is Cybran or Aeon, often insulting them via the comlink.