Guardian angel
A guardian angel was an angel who looked out for the welfare of someone.

Metaphorically, it could refer to a person who did the same. In 2375, Kathryn Janeway noted that  had a guardian angel, namely Harry Kim, whose alternate future self sent phase corrections to Seven of Nine back through time, thereby averting the destruction of Voyager and the deaths of all but KIm and Chakotay. ()

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