Ratchet is the main protagonist of the Ratchet & Clank series, Though in Secret Agent Clank he appears with two personalities, his normal one, and one brought on by a special device. When the device activates and turns him evil, he is known as the Mastermind. He is Ratchet's dark side.
The Mastermind sneaks into the boltaire museum and steals the eye of infinity but is arrested and taken to prison after sending it away.
On his way to prison he is interviewed and he gives a story as to why he stole the eye and hints at his plans.
In Prison the Mastermind causes a riot and reveals that if he is not given a planet to rule he will destroy the galaxy.
After Klunk's defeat, Clank quickly destroyed the device on Ratchet's head so that he could stop the Mastermind from returning.