1. one who undoes or reverses something
Usage: formal
2. one who causes ruin or destruction
Usage: literary

Examples

• The new manager became the undoer of all the previous reforms.
• Time proved to be the undoer of their carefully laid plans.
• He was his own undoer, making choices that led to his downfall.
• The scandal was the undoer of her political career.
• Critics called him the undoer of decades of environmental progress.
• Pride was the undoer of many great leaders throughout history.