History in Kingdom HeartsWhen Vexen was given the assignment to create clones of the keyblade wielders to serve as the Organization XIII's elite warriors capable of freeing hearts from the heartless, one of the keybearers he gained DNA from was that of King Mickey Mouse. However, too much Heartless DNA was inserted into the clone during its creation, frying its brain circuits and rendering the resulting creature, Julius Mouse, a monstrous failure. Vexen subsequently abandoned the creature to the Realm of Sleep and went on to create the Riku Replica and Xion as replacements for his previous failure. Of course, Julius Mouse would not be contained for long in the Key of Sleep, and Maleficent soon found out about the creature through Vexen's lab notes. She then summoned the creature with her dark magic, and used her powers to make it obedient to her and Pete. Now, Julius Mouse serves as a member of Pete's Gang, and is the Brute of the team.
But then again, Maleficent might have had to look at the notes even further because had she read them more, she would have discovered that Vexen had also created a monstrous clone of Pete to serve as a backup plan should Julius Mouse and the Replicas fail their duty. This clone, like Julius Mouse, was also sealed away in the Realm of Sleep, where Sora encountered him in his hiding place at Traverse Town...and he was named: Julius Pete.