The MCP (Master Control Program) is the highest ranking program in the Hollow Bastion OS.
 Journal Entries
 Kingdom Hearts II
The Master Control Program. He rules the system as the chief control program.Instead of working for the users, the MCP is planning to take over the system for himself. By refusing to follow the users' orders and trying to enact his evil plan, he's causing chaos among the other programs.
The MCP was once the network controlling program of a company called ENCOM, where it was able to monitor and control the progress of functions of the entire company. As time wore on, it began to make itself more powerful by deleting weaker programs and adding their functions to himself. Eventually he was too powerful to be stopped even by a User, and was only stopped from taking total control of every computer network by a lone User who was pushed into the digital realm, with the help of a powerful security program called TRON.
 Ansem's Computer
An unknown amount of time later, the system was copied by Ansem the Wise and used in his personal network. He created a database for information concerning Hearts and the Heartless, protected by TRON. He also rebuilt the laser that allows Users to travel into the computer, and stored away the MCP, realizing the danger it posed to the system, and to Users themselves.
Years later, the Hollow Bastion Restoration Committee rediscovered Ansem's computer and booted it up, discovering the MCP still active. He had been using Ansem's and Xehanort's data to create an army of digital Heartless, under command of his number two Commander Sark. He locked away TRON, and no other programs were ever shown, though were likely either destroyed and replaced by Heartless or out of sight, mindlessly working for the MCP.
 Space Paranoids
The MCP, however, was able to fight from another front to take over the world. He reactivated the Heartless manufacturer in Ansem's lab, and began creating an army of electronic Heartless to ravage the streets of Hollow Bastion. Although Leon and Yuffie fought them off well enough, the Heartless kept coming, and their only hope was TRON, who was locked away in the Hollow Bastion OS. Sora saved TRON in the digital world. After TRON received the enhancement from Cid, he and Sora went to the Central Computer Mesa, and combatted the MCP himself, as well as a gigantic Sark.
TRON was eventually able to use Cid's program to delete the MCP, and he quickly jumped into the Master Control Program's resting place, seemingly killing himself. He is soon shown to have taken over the MCP's job, however, and now runs the entire system according to the wishes of the Hollow Bastion Restoration Committee. He also gives them a brief glimpse of what the world used to look like, and allowed them to remember the town's real name, Radiant Garden.