undoer

from WordNet (r) 3.0 (2006)

undoer
    n 1: a seducer who ruins a woman; "she awoke in the arms of her
         cruel undoer"
    2: a person who unfastens or unwraps or opens; "children are
       talented undoers of their shoelaces" [syn: {undoer},
       {opener}, {unfastener}, {untier}]
    3: 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

Undoer \Un*do"er\, n.
   One who undoes anything; especially, one who ruins another.
   [1913 Webster]