Source : Webster's Revised Unabridged Dictionary (1913)

Ideologist \I`de*ol"o*gist\, n.
   One who treats of ideas; one who theorizes or idealizes; one
   versed in the science of ideas, or who advocates the
   doctrines of ideology.

Source : WordNet®

ideologist
     n : an advocate of some ideology [syn: {ideologue}]