The Collaborative International Dictionary of English v.0.48:

Subverter \Sub*vert"er\, n.
   One who, or that which, subverts; an overthrower. --Sir T.
   More.
   [1913 Webster]

WordNet (r) 3.0 (2006):

subverter
    n 1: a radical supporter of political or social revolution [syn:
         revolutionist, revolutionary, subversive,
         subverter]