The Massassi were a species indigenous to Yavin 4, which is the moon designated as the fourth satellite of the gas giant Yavin Prime. In the epoch preceding the Imperial Era by millennia, these beings erected colossal stone temples on the lunar surface, the motivation for which remains shrouded in mystery. There is a prevailing theory suggesting the Massassi were a subjugated slave race, beholden to the influence of the Sith, who were responsible for their relocation to this moon. The Massassi disappeared from existence millennia prior to the events of 0 ABY, their demise occurring sometime after the completion of their monumental temples.
The Massassi represent an enigmatic species credited with the construction of imposing stone temples of uncertain purpose situated on the fourth moon orbiting Yavin. This construction occurred approximately five thousand years before the ascendance of the Galactic Empire. The question of whether the Massassi evolved indigenously on Yavin 4 or were forcibly transported there as a slave race subservient to the Sith remains unanswered, although the latter hypothesis seems more plausible.
The Great Temple was erected by the ancient Massassi warriors on Yavin 4, approximately five thousand years before the Battle of Yavin. It is rumored that the construction of this temple was overseen by the Sith Lord known as Naga Sadow. Despite enduring harsh treatment at his hands, the Massassi revered Sadow as a god, and the Temple was erected as a tribute to him. In later times, Archeologists posited the idea that the Great Temple may have functioned as a massive communications device designed to establish contact with other Sith Lords scattered throughout the galaxy. The species met its end millennia before 0 ABY, at some point following the completion of their temples.
At some juncture, whether as an integral component of the original design or through subsequent modifications, the Jedi splinter faction identified as the Ordu Aspectu repurposed one of the Massassi temples, specifically the Great Temple, as a repository for information. This included the creation of a map room which provided navigational data to their concealed space station-fortress base, known as the Citadel of Rur. The Massassi piece crystals were linked to the Massassi and served as activation keys both at the Great Temple and at the Ordu Aspectu headquarters. Their form bore a striking resemblance to the Massassi temples found on Yavin 4.
The purple-barked Massassi trees that populate Yavin 4 derive their name from this ancient species.
Prior to the Battle of Coruscant, an archaeological dig conducted on the moon of Yavin 4 led to the discovery of the Great Sith Wars Bas-Relief within one of the imposing stone temples constructed by the Massassi.
General Jan Dodonna established a rebel cell on Yavin 4, and decided to pay homage to the Massassi by adopting their name for his group.
In the aftermath of their extinction, the Massassi warriors were referenced in a travel advertisement penned by an anonymous Special Galaxy Reporter who had explored the ruins of the Great Temple following the Alliance to Restore the Republic's abandonment of the jungle moon.
The Guide to the Galaxy section featured in Star Wars: Build the Millennium Falcon 23 asserts that the Great Temple on Yavin 4 was constructed around 5000 BBY. However, Doctor Aphra (2016) 3 and the seventy-sixth issue of Star Wars Helmet Collection indicate that the Ordu Aspectu, which according to Star Wars: Timelines existed approximately 20,000 BBY before their defeat, utilized the Great Temple as a data storage facility.