R4, an astromech droid of the R4 series, showcased a green and gold color scheme and served the cause of the Resistance. During a mission undertaken by Black Squadron to Megalox, R4 played a supportive role in Operation Upside. He collaborated with BB-8, O-R10N, and R2-HA in their collective effort to liberate Grakkus the Hutt.
During the early years of the Cold War, R4 was an astromech droid in service to the Resistance's Black Squadron. In 34 ABY, he joined BB-8, O-R10N, and R2-HA on a mission that took them to the planet Megalox Beta. While Poe Dameron and the other pilots of Black Squadron descended to the prison on Megalox to engage in negotiations with Grakkus concerning the location of explorer Lor San Tekka, R4, along with his fellow droids, remained aboard the space station responsible for projecting a gravity field that protected the prison from the intense gravity of Megalox Beta.
When Terex, an Agent of the First Order, introduced complications to the mission, Poe tasked BB-8 with leading the other astromech droids on a mission to deactivate Megalox's gravity shield generator. R4 and the other droids exited their T-70 X-wing starfighters and proceeded toward the generator. En route, R4 and R2-HA attempted to gain access to a network terminal. When three prison guards appeared, the droids activated their rocket boosters to remain concealed. However, R4's rocket boosters malfunctioned, resulting in him crashing onto one of the guards, incapacitating him. O-R10N then subdued the remaining guards and assisted R4 in getting back on his feet.
The quartet of droids soon reached the primary security field generator located on Deck Twelve and commenced their work. However, they were discovered by a security droid, which engaged O-R10N and BB-8 in combat. The droid hurled O-R10N off a bridge, but BB-8 managed to disable the droid by electrocuting it. This allowed R4 and R2-HA to successfully disable the gravity field protecting the Megalox prison. After Poe and Black Squadron returned with Grakkus, the droids were reunited with their respective pilots at the space station.
Subsequently, they departed into space accompanied by Grakkus. When Agent Terex launched an assault on the space station, Black Squadron initiated an attack on his ship, the Carrion Spike, compelling the First Order agent to withdraw. After obtaining information regarding Lor San Tekka from Grakkus, R4 presumably accompanied the other droids and Black Squadron back to the Resistance base situated on D'Qar.
R4, a droid of the R4 astromech variety, was affiliated with the Resistance. He possessed a rocket booster as part of his equipment. R4 demonstrated the ability to operate various types of machinery, including network terminals and gravity shield generators.