The idea of using jet packs to fly first emerged in the 1920’s in science fiction publications. Later, in the 1950’s scientists built one of the earliest jet packs called a Jetvest during World War 2. The Jetvest was never mass produced though due to a lack of funding for further development.

https://www.pocket-lint.com/gadgets/news/142963-the-history-and-future-of-jetpacks-mankind-s-obsession-with-personal-flight-in-photos