Based on this episode a number of trivia books have claimed that 99's real name is Susan Hilton. However 99 herself denies this, telling Max that Susan Hilton was the cover name she was using when she met her future fiancee.
This episode features one of the worst matches of interior and exterior shots ever. The interior of the 3rd Street Bank has an entrance where the glass doors face a green marble wall no more than a few feet away that completely blocks the view, whereas the exterior of the same bank has an entrance opening on to a wide open sidewalk and parking lot with a concrete canopy supported by black metal pipes.
Max's imposter is shown studying a movie clip of Max's daily habits and mannerisms. In the clip, Max is shown sitting on his bed with his bedroom door situated at his far left. However, in actuallity, Max's bedroom door is located directly across from the bed -- not to the left of the bed.
The Gunman is played by James Komack who directed many episodes of Get Smart (including this one).
This episode was chosen to represent Get Smart! in July of 1995 when Nick at Nite aired a week-long marathon of shows from previous seasons to celebrate NaN's 10th anniversary.
This episode was co-written by Don Adams with his sister Gloria Burton.
The plot of a commoner impersonating a nobleman to whom he bears an uncanny resemblance was first popularized in Anothony Hope's novel "The Prisoner of Zenda". The novel was adapted into a celebrated movie in 1937 starring Ronald Colman as the identical king and commoner. Since Don Adams has said that his famous Maxwell Smart voice developed out of a Ronald Colman impression, a take-off of the movie must have seemed almost inevitable.
This episode marks the debut appearance of CONTROL's showgirl/chemist Dr. Steele.
In this episode we learn the Chief is married when Max mentions his wife.
In a cameo, Bill Dana appears as a man on the street Max approaches as he tries to find someone who speaks Spanish. The fact that Dana's character doesn't speak Spanish is an inside joke on the fact that Dana's most famous character was the Spanish speaking Jose Jimenez. Additionally, Don Adams got his start on Dana's show and Dana helped Adams develop his trademark 'Would you believe?' routine.
As an inside joke, the airport announcer says, "Mr Buck Henry, please pick up your poodle at baggage claim." Buck Henry co-created Get Smart with Mel Brooks.
In the DVD introduction to this episode Barbara Feldon mistakenly says this episode's title is taken from "a famous Hitchcock thriller". The 1957 movie Witness for the Prosecution was actually directed by Billy Wilder.
This episode and the next two episodes were co-creator Buck Henry's final episodes as story editor. After the episodes aired, Henry left the series to co-write the screenplay for the 1967 film "The Graduate."
Smart reads his horoscope and is a Scorpio.
The Chief says that Goldwater lost the 1964 presidential election by 17 million votes. He actually lost by 15.9 million votes.
Max and 99 lay down on the front seat of the car right before bullets are shot through the windshield. When Max and 99 sit back up, a shadow suddenly appears on the wall behind them, revealing that time lapse photography was used.
Goof: Dr. Ratton is killed in this episode. However, in Season 3 episode "When Good fellows Get Together" Dr. Ratton is alive and well.
Goof: When Smart tries to make a pool shot to impress The Chief, he rips the felt near the side pocket. When they show the table again the rip is no longer there. In subsequent shots it has reappeared.
The character Willie Marconi is based on real-life pool legend Willie Mosconi.
Max mentions that he learned a trick shot in pool from someone named "Three Fingers" Yarmy. The name Yarmy is the real last name of Don Adams.
At the end of this episode, the British agent says he has come from Scotland Yard. But Scotland Yard is not a secret organization; the British external affairs branch is MI6.