Sherlock Holmes and Dr. Watson are both played by actors who had played the roles in other productions; Douglas Wilmer had played Sherlock in the first series of The BBC's Sherlock Holmes from 1964-65 (with Nigel Stock as Watson), while Thorley Walters had played Watson in the 1962 film Sherlock Holmes and the Deadly Necklace (with Christopher Lee as Sherlock).
Gene Wilder was an accomplished college fencer and gets to show off his swordfighting skill in this film.
Real-Life Relative: Aubrey Morris (Coach Driver) and Wolfe Morris (Frenchman) were brothers in real-life.
What Could Have Been: Gene Wilder asked Mel Brooks to direct. Brooks declined, stating that he would find it difficult to direct a screenplay that wasn't his own conception. Brooks did say though that Wilder should go off and make this film, could call upon him day or night, and after making this movie, he better "come back home as soon as you're done!" He did have a cameo as the voice of departing assassin after choosing the "lady" door over the "tiger" door, only to discover they're both tiger doors.