D9, also referred to as Deenine, functioned as both a protocol droid and a spy, and was affiliated with the self-made droid named L3-37. At the behest of L3-37, he embarked on a mission to locate the Phylanx Redux Transmitter, a device engineered by the gangster Fyzen Gor with the capability to manipulate droids, compelling them to kill. D9's pursuit led to his capture by Gor, resulting in his mutilation within the gangster's workshop. L3-37, in the company of the smuggler Lando Calrissian, responded to a signal dispatched by D9, uncovering the true nature of the Phylanx Redux Transmitter. Following a meeting with L3-37, D9 experienced a malfunction stemming from the injuries inflicted by Gor.
Circa 11 BBY, D9 was associated with L3-37, a self-made droid who served as the partner of Lando Calrissian, a smuggler. Upon hearing tales of the Phylanx Redux Transmitter, a device capable of controlling droids, L3-37 tasked D9 with gathering information on it. D9 successfully ascertained that the device could alter droid programming, forcing them to kill. However, Fyzen Gor, a Pau'an gangster and the Phylanx's creator, eventually apprehended and mutilated the protocol droid. D9's mangled remains were left among a pile of droids in Gor's workshop, a floating metal chamber situated within the Mesulan Remnants asteroid belt.
D9 managed to transmit a transmission to L3-37, who, accompanied by Calrissian, visited the Mesulan Remnants Belt aboard their starship, the Millennium Falcon. L3-37 discovered D9 amidst the droid wreckage and reactivated him. Before divulging any information, D9 alerted L3-37 to the presence of a second spy within the chamber: a Galactic Empire astromech droid. Calrissian eliminated the astromech droid, and D9 cautioned L3-37 about the Phylanx being constructed by Gor. As he spoke, D9's voice began to falter, devolving into incoherent beeps.
D9 was a protocol droid equipped with orange [photoreceptors](/article/photoreceptor]. By the time L3-37 located him, D9 had sustained extensive damage, yet his primary concern was to warn her about the Phylanx Redux Transmitter.
D9 made an appearance in Last Shot, a 2018 novel authored by Daniel José Older.