The ongoing mission of the Star Wars franchise is expanding upon minor details, drawn up by artists in the 70s, to create endless content from fan-favorite concepts. There are seemingly infinite questions left unanswered, and so long as they find interesting answers, fans will stay tuned every time.
The Book of Boba Fett wasn't the biggest success of the franchise and its failure was an interesting one to watch. Though Fett once remained a popular character because of his unique mystery, delving in too deeply can ruin the magic. Fans saw in Attack of the Clones that a young Boba Fett claimed his armor from his father's corpse, but the franchise has barely depicted how Jango got ahold of that sacred piece.
Jango Fett was a Mandalorian. He got the distinctive Beskar steel armor and attached weapons systems the same way every other warrior of the clan did; he earned it. Jango fought in the Mandalorian Civil War as a Mandalorian Commando. He was a foundling, just like Din Djarin long after him. It's unclear exactly who his parents were when he was acquired, or what led to his mysterious adoption by Mandalorian hands. What is known is that Jango was born on Concord Dawn, a mostly destroyed planet located in the corner of the galaxy owned by Mandalore. Somehow, from humble beginnings in a shattered world, Jango excelled as a warrior and later turned his attention towards bounty hunting. It's the period between his birth and his bounty hunting career that remains shrouded in mystery.
Foundlings are common amongst Mandalorian society, as their intricate code forbids them from leaving an abandoned child without a home. It is canon that Jango had a mentor to teach him the ways of the Mandalorian warriors, but their identity remains a bit questionable. In the old continuity, the one dropped with Disney's acquisition of the franchise, a comic introduced him as Jaster Mereel. Though this was no longer canon, Chapter 14 of The Mandalorian may have brought it back. The first reappearance of Boba Fett sees him reclaim his father's armor, whereupon he brings up its unique holographic sequence to prove to Din Djarin that he's its rightful owner. Some fans claim to have translated the Mandalorian language and found the phrase "mentor Jaste." This is a letter short but does imply that the episode's director Robert Rodriguez might have recanonized Jaster. This is also the episode that finally mentions Jango's foundling status on screen.
The old canon that may be new again places Fett as the son of a farmer who also served as a lawman. His mentor Jaster served the Mandalore sector as a Journeyman Protector and took Jango under his wing after failing to save both of his parents. Jaster became the Mand'alor, the single leader of the planet and its people. He achieved that rank through sheer warrior skill, but his reign was challenged by the violent Death Watch faction. Jaster later died in front of his new adoptive son but passed his code of honor and rank on to him. This would mean that Jango briefly led the Mandalorians, but it's unlikely that this will be canon in the modern incarnation.
Perhaps the most frustrating thing about Jango Fett's backstory is that it is contested within the story. Tons of characters' stories have multiple interpretations or ambiguous details, but Jango Fett's life story is disputed in fiction by other Star Wars characters. It is known that Jango left Mandalore at some point to pursue a career in bounty hunting. In his absence, a pacifist leader named Almec rose in the ranks to become the prime minister of the planet for many years. When asked about Jango, he described him as an unaffiliated bounty hunter who came upon Mandalorian armor through unknown and probably illicit means. This ambiguity is difficult, every piece of Jango's backstory is supported by one or two lines of dialogue. There are extremes in the interpretation of his life's story, whether he was always a selfish hunter or once served as leader of a proud warrior race. Based on Boba Fett's appearance in The Mandalorian, the real answer is probably somewhere in the middle.
Jango Fett was a Mandalorian who fought in one of the planet's countless civil wars. He earned his Beskar armor, and it served him well for his entire life, even though he abandoned his original lifestyle. After his death at the hands of a Jedi, a classic nemesis of his people, his armor went on to serve his progeny for his entire life. Jango Fett is a minor character, more known for what he brought into existence than for anything he actually did, but he still has an interesting story. Even if that story is disputed by fans, dueling canon, and other characters in the story.