lifesaver
n.something that helps you survive or solves a very difficult problem. You use this to describe a person or thing that is extremely useful in a dangerous or stressful situation.
n.a person or thing that provides essential help or relief in a critical situation. Often used figuratively to describe a solution to a significant problem.
“The new software was a lifesaver for our busy team.”
“When the car broke down on the highway, the roadside assistance service was a lifesaver for the stranded family.”
“The discovery of the ancient manuscript proved to be a lifesaver for the historian, providing the missing evidence required to complete her decades-long research project.”
From life + saver.
Etymology adapted from Wiktionary, available under CC BY-SA 4.0.