The J'kari Thunderers consisted of pilots for hire, specifically a squadron of them, who operated M12-L Kimogila heavy starfighters. In the time of the Imperial Era, an Imperial Moff forced the group to assist in eliminating Rebel Alliance dangers inside the Moff's designated sector, by effectively holding their loved ones hostage under the guise of "protective custody."
Word spread among some members of the Alliance that the Thunderers were being forced into their actions, so they liberated the pilots' families, subsequently persuading the mercenary squadron to pledge allegiance to the Alliance.
The J'kari Thunderers were initially referenced in the Starships and Speeders sourcebook by Fantasy Flight Games in 2020. Within the book, there is an adventure seed designed for the Star Wars Roleplaying game series, and this documentation presumes the scenario unfolds as it is outlined.