The person responsible for extras casting was Jewish and was casting a lot of his friends and relatives in tiny parts. As a result, when the military consultant (from the KGB) saw the chosen actors, he said that most of the guards at Nazi headquarters looked like soldiers of Israeli army, not elite SS soldiers, and demanded that they change them to more appropriate looking actors. As a result, the roles of SS guards were played by military cadets of the frontier-guards schools from Tallinn (Estonia) and Riga (Latvia), who, being tall, blonde and blue-eyed looked more like real SS soldiers.
Archil Gomiashvili was so eager to play Stirlitz that he invited the crew to a restaurant. During the night, Yulian Semyonov even told Tatyana Lioznova that Gomiashvili was the perfect Stirlitz. In the end, however, the role went to Vyacheslav Tikhonov. Another contender for the role was Oleg Strizhenov.
According to the original book, Stirlitz was single and had a girlfriend abroad. The scene of Stirlitz's short date with his wife was Tatyana Lioznova's idea. When she showed footage to the crew, Yulian Semyonov agreed it was very good and was very frustrated that he didn't write the scene.
After the series was released, Stirlitz became the subject of numerous Russian jokes and remains one of the most popular Russian joke characters until today. Most of the jokes spoof the solemn style of the voice-overs from the series and their plot is resolved in grotesque plays on words or in dumb parodies of Stirlitz's overly smart narrow escapes and superlogical trains of thought.
There were no characters of Frau Saurich and Gabi in the original novel. Tatyana Lioznova's idea was that Frau Saurich could remind Stirlitz of his mother and, reserved as he was, he could slightly reveal himself before her. Lioznova didn't like the scenes with Frau Saurich that Yulian Semyonov wrote and she decided she would rewrite the script during filming, but nevertheless, they showed the script to Faina Ranevskaya and she rejected the offer to play Frau Saurich. The role went to Emiliya Milton. Her lines were written right on set but Lioznova liked her performance so much that when some scenes with Milton were completed, Lioznova would sit down and write more.