This article is from the NARF--The Nifty Animaniacs Reference File FAQ, by Lee Cremeans email@example.com with numerous contributions by others.
Yes you did. Brain's voice is a parody of Orson Welles done by
Maurice LaMarche, who also does voices for "The Critic". For ED
WOOD, Mo's voice was dubbed in. Someone else played the part of
Orson in the movie.