Source : Webster's Revised Unabridged Dictionary (1913)

Ruiner \Ru"in*er\, n.
   One who, or that which, ruins.

Source : WordNet®

ruiner
     n : a person who destroys or ruins or lays waste to; "a
         destroyer of the environment"; "jealousy was his undoer";
         "uprooters of gravestones" [syn: {destroyer}, {undoer}, {waster},
          {uprooter}]