Conservator

n.
  1. One who preserves from injury or violation; a protector; a preserver.
    1. An officer who has charge of preserving the public peace, as a justice or sheriff.
    2. One who has an official charge of preserving the rights and privileges of a city, corporation, community, or estate.
    Conservators of the River Thames ,
    a board of commissioners instituted by Parliament to have the conservancy of the Thames.