Fantozzi's daughter is actually played by a man because the creators wanted to make Mariangela look as ugly as possible, like in the book.
The character of Fantozzi is so popular in Italy that the widely used adjective "fantozziano" means "someone or something as unlucky as Fantozzi."
Fantozzi was a great financial success, collecting more than six billion lire and remaining in first run for more than eight months and being the highest-grossing movie in Italy of the 1974-75 film season
In 2004, with the release of the DVD-Video edition, a scene cut from the film version was reinstated. The scene is located immediately after the tennis match with Filini and shows Fantozzi's first attempt to lose weight. The scene was then removed again from the restored cinematographic edition in 2015. In Fantozzi contro tutti (1980) the scene was reproposed, expanded, and set in the same location (the Monumental Hospice of San Michele a Ripa in Rome) as the first movie.
Paolo Villaggio wrote Fantozzi's short stories for the weekly L'Europeo. These were collected in the book "Fantozzi" (1971), which sold over 1 million copies and inspired the film.