Source : Webster's Revised Unabridged Dictionary (1913)

Liberator \Lib"er*a`tor\ (l[i^]b"[~e]r*[=a]`t[~e]r), n. [L.]
   One who, or that which, liberates; a deliverer.

Source : WordNet®

liberator
     n : someone who releases people from captivity or bondage [ant:
         {captor}]