Experiment R was a character in The Mary Morstan Mysteries portrayed by Martin W. Payne. He is a failed experiment of Professor Moriarty, and his sole purpose was to test his infamous "Simian Serum", a potion designed to enhance the drinkers strength and agility. However, the serum took a very long time to perfect, and claimed the sanity of countless test patients, both willing and not.
Little is known about who Experiment R once was, but it is thought the letter R is the first name initial of whoever he once was, for this was the case for Thomas Digweed being referred to as Experiment T by Moriarty.
Experiment R appeared in the series finale "The Devil's Gambit" (Series 2, Episode 5) in which he is used as a secret weapon by Moriarty to dispose of Lord Booswar.
- "Pass....the....mustard....must past the mustard, must pass the mustard!!"
- "Must dust, must be clean, clean, dust, dust, dust"