der Lebensretter
lifesaver
A person who saves another person's life in a life-threatening situation.
Der Feuerwehrmann wurde als Held und Lebensretter gefeiert.
The firefighter was celebrated as a hero and lifesaver.

lifesaver
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lifesaver
A person who saves another person's life in a life-threatening situation.
Der Feuerwehrmann wurde als Held und Lebensretter gefeiert.
The firefighter was celebrated as a hero and lifesaver.

The word is a compound of 'Leben' (life) and 'Retter' (rescuer). A 'Retter' is a person who rescues someone. So a 'Lebensretter' (lifesaver) is literally a person who saves a life.
Durch die schnelle Hilfe wurde der Sanitäter zum Lebensretter.
Through his quick help, the paramedic became a lifesaver.
You can recognize the colloquial meaning by the fact that it often refers to a thing or person that helps in a situation that is not life-threatening but very unpleasant.
Danke für den Regenschirm, du bist mein Lebensretter!
Thanks for the umbrella, you're my lifesaver!
The meaning 'Rettungsschwimmer' (lifeguard) becomes clear from the context. Watch for words like 'Schwimmbad' (swimming pool), 'Strand' (beach), 'See' (lake), or 'ertrinken' (to drown).
Am Badesee passte ein Lebensretter auf die Schwimmer auf.
At the swimming lake, a lifeguard watched over the swimmers.
Using the word for help in a difficult situation is clearly colloquial. In formal texts, this metaphorical meaning would be avoided.
Diese Kopfschmerztablette ist heute mein Lebensretter.
This headache tablet is my lifesaver today.
hero
'der Held' and 'der Lebensretter' can both describe a person who has done something very brave. But a lifesaver is more specific: they really saved someone's life in a dangerous situation. A hero can also be someone who acts bravely, helps others, or is admired in a story, without necessarily saving a life. So you can often call a lifesaver a hero, but not every hero is a lifesaver.

Der Lebensretter zog das Kind aus dem kalten Wasser.
The lifesaver pulled the child out of the cold water.
Nach dem Brand nannten viele Menschen den Feuerwehrmann einen Helden.
After the fire, many people called the firefighter a hero.