Years ago my friend Mike Zuhl predicted the day that CGI characters would be developed independently of films and then cast into roles when needed. Are we there yet?
Colbert played a cameo roll in a recent Lord of the Rings film. Did he play his fabricated character there? I think not. Not yet.
Stephen Colbert commands a daily audience by pretending to be something he is not for comedic effect. In this near final show he interviews Smaug the fire-breathing dragon from Lord of the Rings, also a creation of the imagination. video 
The spot was humorous even for someone not familiar with the literature or the film.
The CGI was impressive especially considering they had to work within the constraints of the daily television format.