preemptor

/priˈɛmptər/
noun
  1. A person or thing that takes action to prevent something from happening, especially to gain an advantage.
    • As a preemptor of conflicts, the diplomat worked to stop disputes before they escalated.
    • The company was a preemptor in the market, launching its product before any competitors.
    • The early bird is often a preemptor, securing the best seats before anyone else arrives.