(not) half the person/man/woman (one) used to be
Having a reduced, diminished, or weakened physique, disposition, conviction, prowess, or mental acuity, as after some action, event, or trauma. Sometimes used in the negative but to the same effect. Poor Mary, she isn't half the person she used to be since that car accident. Have you seen John lately? He lost so much weight that he's like half the man he used to be!