ruiner

from WordNet (r) 3.0 (2006)

ruiner
    n 1: a person who destroys or ruins or lays waste to; "a
         destroyer of the environment"; "jealousy was his undoer";
         "uprooters of gravestones" [syn: {destroyer}, {ruiner},
         {undoer}, {waster}, {uprooter}]

from The Collaborative International Dictionary of English v.0.48

Ruiner \Ru"in*er\, n.
   One who, or that which, ruins.
   [1913 Webster]