Important note: it might be a good idea to start with the 2nd episode of this mini-series (Adventures of the Little Domovoi) which serves as a prequel to the rest of the story. And yes, it is among the most popular Soviet cartoons. Quite rare for a stop motion film as children generally hated them. Also, unlike Cheburashka, it was produced by Studio Ekran known for its lower-budget made-for-TV animation. And yet it's a true labor of love.
Kuzya (or Kuz'ka, "you may call me Kuzen'ka as well - I'm still young, only 700 years old") was originally a character of several comedy books by Tatiana Aleksandrova who mixed Slavic folk creatures (Domovoi, Leshy) with modern-day realias. A naughty underage house spirit had to guard home without revealing himself, but was immediately spotted by a bored girl who became his tour guide in the high-tech Soviet world.
Only one novel was published during the author's lifetime, with ugly black-and-white drawings added despite she prepared her own illustrations, being a professional artist. But they weren't accepted, the book didn't sell well. And in 1983 Aleksandrova died of illness aged 54. Her husband Valentin Berestov swore on her grave to publish all novels. Same day the Ekran Studio contacted him regarding an animated adaptation of the fairy tale. Berestov wrote the screenplay, and by the next year the film was ready.
Not only it stayed true to the text, but also the art style was inspired by Aleksandrova's drawings. And while the animation wasn't as smooth as some of Soyuzmultfilm's projects, the film hit the spot. Kuzya voiced by the popular comedy actor Georgy Vitsin was both cranky and adorable, the hilarious writing and non-stop action kept kids glued to the screen, while the postmodern mix of past and present (Kuz'ka even speaks with a village accent, inserting outdated words) made it very quotable.
It was followed by three films, with many characters such as Baba Yaga and her sarcastic cat added along the way, while the remaining novels were finally published - all to a great success. Thus Berestov's dream was fulfilled and Aleksandrova's writings became part of Russian culture, all thanks to this wonderful little gem.