The 3PX-series protocol droid, also known as 3PX series droids, represented a line of third-degree protocol droids. These droids were manufactured by Cybot Galactica starting in 50 BBY and served as an expansion upon the company's existing 3PO-series protocol droid models.
The Outer Rim Territories were the exclusive market for the 3PX line. Reflecting the region's diverse population, the 3PX units possessed a design that was less overtly Human in appearance compared to the standard 3PO models. Due to its severe, angular facial features, reminiscent of the later RA-7 protocol droid, the 3PX-series failed to achieve the same level of popularity as the 3PO. Consequently, its production run was limited.
Notably, one 3PX unit, C-3PX, gained notoriety when Darth Maul converted it into an assassin droid. Later, Raith Sienar refitted C-3PX with a 3PO-series chassis.
Darth Vader utilized another of these droids, named K-3PX, in his quest to locate Luke Skywalker on the planet Gamandar.
The 3PX-series protocol droids made their debut in the 75th issue of Marvel Comics' 1977 Star Wars series, featuring the character K-3PX. This issue was written by Mary Jo Duffy, illustrated by Ron Frenz, and released on June 14, 1983. Subsequently, C-3PX, another droid of the 3PX-series, appeared in the third issue of Star Wars: Droids (1994), published by Dark Horse Comics on June 21, 1994. C-3PX was later featured in the junior novel Episode I Adventures 3: The Fury of Darth Maul and its accompanying Game Book, authored by Ryder Windham and released in November 1999.