Yavin 4 is a rainforest moon orbiting its gas giant, the Yavin star system. The moon is the site of a secret Rebel base. It is also a formerly Sith-dominated planet due to the presence of Sith temples. It was the home of the now-extinct species known as the Massassi.
Originally the home of the alien species known as the Massassi, Yavin 4 fell into the folds of the Sith Empire some 5,000 years before the advent of the Galactic Civil War. For unknown reasons, the Massassi species went extinct by the time of the Galactic Empire, leaving only the great pyramid-like temples they built behind.
Anakin Skywalker met and fought Asajj Ventress for the first time on Yavin 4. Years later, the Rebel Alliance established a base here, and during Grand Admiral Thrawn's attack on Atollon, evacuated to Yavin 4.
When Leia Organa returned to Yavin 4 with the plans to the Death Star, they found that they could destroy it by firing into an unshielded exhaust port. When the Death Star arrived in the system, the Alliance sent X-wings and Y-wings to destroy the battle station. Grand Moff Tarkin was convinced of the station's invincibility and did nothing. Darth Vader, however, realized the danger and went out to stop the Rebels. Vader was about to blast Luke out of the air when Han Solo blasted him away. Luke fired into the port and destroyed the Death Star winning the Battle of Yavin for the Rebel Alliance. Several battles were later fought on its surface as the Empire launched its counterattack.
After the Galactic Civil War ended, Rebel operatives Shara Bey and her husband Kes Dameron, the parents of Resistance pilot Poe Dameron, settled down on the moon, planting a branch of a Force-sensitive tree given to them by Luke Skywalker in the moon's soil.