The Mandalorian foundling and bounty hunter Jango Fett received instruction from a mentor before his death at the First Battle of Geonosis in 22 BBY. A fragment of this mentor's identity was inscribed in the Mando'a script within the chain code belonging to Jango's clone offspring, Boba. This partial spelling appeared as "Jaste."
This mentor was alluded to in a hologram featured in "Chapter 14: The Tragedy" of The Mandalorian, a Disney+ series created by Jon Favreau and directed by Robert Rodriguez. This episode, which premiered on December 4, 2020, presented a partially obscured name, making full identification challenging.
Within the Star Wars Legends continuity, Jango Fett's mentor is identified as Jaster Mereel, a Journeyman Protector. He was initially introduced via flashbacks in the comic Jango Fett: Open Seasons 1, penned by Haden Blackman, illustrated by Ramón F. Bachs, and released in 2002 by Dark Horse Comics.