Edith Keeler

Edith Keeler ran a soup kitchen for bums in New York City in 1930. Leonard McCoy, accidentally injured, was sent into the past by the Guardian of Forever. He saved Edith's life, thus changing the course of history. James Kirk and Spock had to return to prevent the change, which was complicated when James Kirk fell in love with Edith. Despite her goodness, Kirk had no option but to prevent McCoy from saving her life, letting her die so that the world they knew might still exist. (A Complete Character Guide to Star Trek (Book 2))