1.
lifesaver; one's savior; person to whom one owes one's life
A person who saved someone's life, either literally or figuratively. Can be used for someone who rescued another from mortal danger or who provided crucial help in a dire situation.
Usage
A set expression that can be used both literally (someone who physically saved a life) and figuratively (someone who provided crucial help when one was in serious trouble). The phrase carries a strong sense of gratitude and indebtedness.