warlord

warlord
    n 1: supreme military leader exercising civil power in a region
         especially one accountable to nobody when the central
         government is weak
    

24 Moby Thesaurus words for "warlord":
      Simon Legree, absolute monarch, absolute ruler, all-powerful ruler,
      arrogator, autarch, autocrat, caesar, commissar, czar, despot,
      dictator, disciplinarian, driver, duce, hard master, martinet,
      oligarch, oppressor, pharaoh, slave driver, stickler, tyrant,
      usurper