A computer built by an ancient lawgiver of Beta III, which kept its society docile for six thousand years until Kirk talked it into destroying itself.
Landru was a philosopher who, some six thousand years earlier, ended war on Beta III by creating a machine to guide his people. Long after his death, the computer continues in his name, absorbing the population into a placid collective called the Body and enforcing order through robed Lawgivers, broken only by the violent Festival.
The Enterprise arrives seeking the USS Archon, lost there a century before. When the landing party resists absorption, Kirk and Spock confront the machine and argue that by stifling creativity it is harming the very people it was built to serve. Unable to reconcile this, the computer destroys itself.