Yavin 4 is a moon of the gas giant Yavin Prime.
Great Sith War
In 344 BTC Yavin 4 was visited by Exar Kun where he fought and was eventually captured by the native Massassi, and sacrificed to a Sith Worm. It was then that Kun fully embraced the darkside, enslaved the Massasi into his new Brotherhood of the Sith and went on to fight the Republic in the Great Sith War.
Jedi Civil War
Prior to and during the Jedi Civil War, Suvam Tan, a former slave of Exar Kun, scavenged Yavin 4 using Yavin Station as a base. In 303 BTC Yavin Station was visited by Revan on a number of occasions, where he came across agents of the Exchange who were extorting Tan.
The final resting place of the Ancient Sith Lord, Naga Sadow, Jedi Knight Barel Ovair and his Padawan, Eison Gynt, visited Yavin 4 in 103 BTC to investigate the tomb of Sadow, their they were attacked and defeated by Massassi and driven deep into the tomb of Naga Sadow, somehow Ovair managed to escape. It later emerged that Gynt was possessed by the spirit of Sadow who travelled to the galactic capital to exact vengeance on Barel Ovair. Ovair fought and killed Gynt and destroyed the spirit of Naga Sadow in drawn out duel on Coruscant. By the Cold War investigations by the Jedi Order discovered that Barel Ovair was an agent of the Sith Emperor who had purposely gone to Yavin to destroy the spirit of Naga Sadow, a pre-emptive strike at enemies the Emperor feared would challenge his reign.