The Imperator was a piece in the ancient board game known as Shah-tezh. The piece was represented by a robed figure on the demesne. No matter how many pieces remain in play, if the Imperator is lost, the game must begin anew to continue.
Sheev Palpatine used the Imperator and its role in the game, when explaining to Gallius Rax his plans for the Contingency, and more specifically, how the Galactic Empire had to die alongside his enemies should Palpatine himself suffer death.
The Imperator is similar in function to the King in chess. In addition, in real life, the term "Imperator" acted as the namesake for the term Emperor (the latter being the Old French spelling of the term).