WARNING: The following contains spoilers for Star Wars: The Mandalorian, "Chapter 14: The Tragedy," streaming now on Disney+.
Thanks to The Mandalorian, Boba Fett is officially back in Star Wars canon. While the original Mandalorian bounty hunter is one of the most popular characters in all of Star Wars, he apparently died unceremoniously in Star Wars: Return of the Jedi, by being kicked into a Sarlacc Pit. However, The Mandalorian just rewrote a bit of history and revealed that he survived that experience through some unknown means.
While the official details of his resurrection are unclear for now, the books and comics of the old Star Wars Expanded Universe reveal what happened with a fair amount of clarity.
After Fett knocked into the Sarlacc pit during Return of the Jedi, Boba was much too strong to submit and found a way to survive, as first revealed in 1983's Star Wars
#81, by Mary Jo Duffy and Ron Frenz. Fett clawed his way out but the trauma gave him short-term memory loss. While he was lost and unconscious in the sand, he was captured by Jawas who mistook him for a droid. Those same Jawas also captured R2-D2, which brought Han Solo and Princess Leia back into the fold with Boba. While breaking out R2-D2, Boba's memory is jogged and he attacks Han Solo. But during the rescue mission, the Sandcrawler was hurling towards the Great Pit of Carkoon and Boba ends up in the Sarlacc's digestive track once again.
His second escape is detailed in 1996's J.D. Montgomery story "A Barve Like That" in the Tales from Jabba's Palace anthology.
While he was slowly being digested, he encountered a telepath by the name of Susejo. Susejo speaks through Boba Fett telepathically and tells Boba stories of the Jedi the Sarlacc has ingested. However, Boba is only interested in survival and isn't going to listen to stories and succumb to death. Boba finds out Susejo gained some control of the monster through telepathy. Boba used this relationship to his advantage and was able to escape with his jet pack. After his second escape, Boba ends up with Dengar, another popular Legends bounty hunter. Boba and Dengar become friends and go on several adventures with each other.
Although details of his canonical survival are still coming to light, a few aspects of these stories seem to be making their way into canon. Cobb Vanth purchased Boba's armor from a group of Jawas in the Tatooine desert, which could be the same Jawas that picked up Boba all those years ago. And now that Boba has his armor back, he's set to help Din rescue Baby Yoda from the clutches of the resurgent Empire, so more details about his official escape may come to light very soon.