Definitions of undoer:

• noun:   a person who unfastens or unwraps or opens

  Example: "Children are talented undoers of their shoelaces"

• noun:   a seducer who ruins a woman

  Example: "She awoke in the arms of her cruel undoer"

• noun:   a person who destroys or ruins or lays waste to

  Example: "Jealousy was his undoer"