Mr. Clown is a birthday clown who appears in "Clown and Out".
He comes to visit Wakko on his birthday. Plotz and Wakko have coulrophobia (called "clownophobia" by Dr. Scratchansniff.). In the story, Wakko causes him much physical harm while Plotz looks on with glee.
Mr. Clown is very similar to Mr. Director, except that as a clown, he's noticeably less serious.
He is voiced by Paul Rugg, the same guy that voiced Mr. Director.