The Mandalorian presented a side of the Mandalorian culture and lore that seemed inconsistent with previously established Star Wars canon, but thanks to The Book of Boba Fett, those perceived lore problems have been fixed. In the most recent episode, Din Djarin takes center stage while Boba Fett takes a week off, and he returns to his coven to set up a big Mandalorian lore dump.
Mandalorians don't appear in any of the Star Wars movies, but Boba Fett's Mandalorian armor inspired a number of Expanded Universe stories to flesh out the Mandalorian warrior people (even though Fett himself isn't actually Mandalorian). Those «Star Wars Legends» stories aren't part of modern Star Wars canon under Disney, so the Mandalorian lore is being rebuilt from the ground up. A lot of it was established in Star Wars animation, and now it's being expanded in The Mandalorian and the most recent episode of The Book of Boba Fett.
Related: Why Din Djarin Can Keep The Darksaber Despite Not Being A Mandalorian
Interestingly, when the Mandalorians debuted in live-action, their culture didn't exactly align with the established canon. They had a religious devotion to something called «The Way» and followed extreme rules such as the fact they never removed their helmets. The reason for many of these perceived inconsistencies in canon surrounding Mandalorian lore was partially explained when Bo Katan appeared in The Mandalorian season 2, but now episode 5 of The Book of Boba Fett brings back The Armorer and Paz Vizsla to explain even more.
In Star Wars Rebels, Sabine Wren gifts the Darksaber to Bo Katan Kryze, giving her the title of Mand'alor and ritual authority to stand to rule of Mandalore, which she desires to wield to rebuild their presence on
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