As an advancement over the standard B1-series battle droid, E4 baron droids functioned as battle droids within the forces of the Trade Federation. The experimental baron droid, conceived by Baktoid Combat Automata, was intended as a versatile security unit. Due to the E4 baron's effectiveness, the Trade Federation contracted Baktoid to enhance the design for mass production, ultimately leading to the creation of the B2-series super battle droid.
Droids of the E4 baron type were large and imposing, possessing considerable strength. Their armor consisted of a robust metal called Arcetron. They could track targets using motion, heat, energy, and sound sensors. A single photoreceptor served as the droid's visual input, capable of emitting a bright spotlight for target identification and tracking. Two dual repeating blaster cannons were mounted on their arms as weaponry. Moreover, they could operate for extended durations without needing a direct link to a Central Control Computer.
Despite being more powerful than previous models, the baron droids had weaknesses. They lacked personal energy shields, making them vulnerable to rapid disabling from sustained fire from a blaster rifle or a precise lightsaber strike. Furthermore, their movements were ponderous and slow.
Obi-Wan Kenobi encountered these droids during his investigation concerning the Black Heth criminal organization on Coruscant. Local Naboo fighters had been battling them in swampy areas and had learned to evade them by watching for their telltale spotlights. Another version of the baron battle droid existed, also utilized by the Trade Federation.
Nute Gunray intended to employ a pair of E4 baron droids as his personal assassin squad, but they were instead deployed in the Battle of Naboo. During the invasion, E4 units patrolled the city of Theed. Even though the Trade Federation Droid Army was defeated, the baron droid's success resulted in a design improvement and the subsequent production of the B2 super battle droids to serve as heavy infantry within the Separatist Droid Army.
Many of the droids remained on Naboo, where Royal Naboo Security Forces soldiers eventually hunted them down. Eventually, a baron droid squad seized control of the planet Arzid, ruling through "the law of the blaster" in 16 ABY.
The baron droids that appear in the 2001 video game Star Wars: Obi-Wan exhibit notable differences from the depiction in The New Essential Guide to Droids, particularly in the appearance of their outer plating and the game version's increased bulk.