Source : Webster's Revised Unabridged Dictionary (1913)

Vindicator \Vin"di*ca`tor\, n. [LL., an avenger.]
   One who vindicates; one who justifies or maintains. --Locke.

Source : WordNet®

vindicator
     n : a person who argues to defend or justify some policy or
         institution; "an apologist for capital punishment" [syn:
         {apologist}, {justifier}]