When Don Adams was negotiating his salary, he had his choice between more money per week and no ownership stake in the show, or less money per week and part ownership. Adams chose the ownership deal and never regretted it considering the series' durable popularity in syndication gave him a regular income even as he struggled with being typecast by it.
It is rumored that Agent 99 was originally supposed to be named Agent 69, but NBC censors deemed it to be too "sexually suggestive". According to Barbara Feldon, this is not true. Her character was originally to be named Agent 100 "because she was one hundred percent", but Buck Henry decided 99 sounded more feminine.
CONTROL and KAOS were supposed to be acronyms, but Mel Brooks and Buck Henry never came up with anything for them to stand for.
This show was the principal inspiration for "Inspector Gadget (1983)," of which the main character was voiced by Don Adams, and was also a bumbling and inept agent. Also, some of the lines from this show, such as "Would you believe..." and "Sorry about that, Chief", were uttered by Gadget on occasions.
When asked how he developed his trademark voice for Agent 86, Don Adams said that it came from watching "The Thin Man" movies starring William Powell and Myrna Loy. After hearing Powell repeatedly say, "Asta! Asta!" he decided to imitate his voice for the character of Maxwell Smart.