expression, noun
lifesaver; person who saved one's life
A fixed expression referring to someone who saved your life; carries deep gratitude.
あの医者は私の命の恩人です。
That doctor is my lifesaver.
火事から助けてくれた彼は、まさに命の恩人だ。
He, who rescued me from the fire, is truly the person who saved my life.