While many people think Boba Fett made his debut in The Empire Strikes Back, he actually made his first appearance in the Star Wars Holiday Special, a made-for-TV movie that came out a little over a year after the release of the first film.
The special involved much of the original cast, including Mark Hamill, Harrison Ford, and Carrie Fisher, helping Chewbacca get back to his home planet in order to celebrate Life Day. Within that special was an animated cartoon called The Story of the Faithful Wookie which introduced Boba Fett.
Although the entire Star Wars Holiday Special has never officially been made available, The Story of the Faithful Wookie is slated to be released on Disney+ next month. Along with that, Genndy Tartakovsky’s Star Wars: Clone Wars – Volume I & II, both seasons of Star Wars: Ewoks, as well as the live-action Ewok TV movies, Caravan of Courage and Ewoks: The Battle for Endor, will debut as well.