Lifesaver

Full definition of lifesaver

Noun

1. Someone or something that saves lives.
• 1913, Joseph C. Lincoln, Mr. Pratt's Patients Chapter 7, “… if you call my duds a ‘livery’ again there'll be trouble. It's bad enough to go around togged out like a life saver on a drill day, but I can stand that 'cause I'm paid for it. What I won't stand is to have them togs called a livery. …”
2. My dad loves his job as a surf lifesaver.   Paramedics are not just ordinary workers, but lifesavers with a very important job.
3. (figuratively) Someone or something that is very useful or helpful.
   Thank you so much for fixing my car; you're a real lifesaver!   This shop is a lifesaver on a hot day when you're craving a cold drink.