I believe Ayn Rand admired Cooper more for his conformity to the physical ideal of masculinity than for his acting. Personally, I think he was a poor actor, the Kevin Costner of his era. Sadly, this movie simply could not be The Fountainhead with him at the helm.
With all due respect to those who have stated otherwise, I also believe that the actor who portrayed Toohey really didn't "get it." In the novel, Toohey is so dangerous because of his misapplication of great insight and intellect (driven by his bankrupt core values). The actor in the movie to my view played him more as a straig