11-4D served the Sith Lords Darth Plagueis and his apprentice Darth Sidious. After Darth Sidious killed his master, 11-4D continued serving Sidious in several guises. In public, Sidious assumed the persona of Senator Sheev Palpatine of Naboo who eventually rose to the position of Supreme Chancellor following the Battle of Naboo. Sidious manipulated the Separatist Crisis which led to the emergence of the Confederacy of Independent Systems and the devastating Clone Wars. Sidious used the clone Grand Army of the Republic to destroy the Jedi during the Great Jedi Purge. He then appointed himself Emperor and transformed the Republic into the first Galactic Empire.
By 14 BBY, 11-4D was stationed at the Imperial Palace, which had been the former Jedi Temple. 11-4D also spent time with his master inside Sidious' lair, a small rock-walled enclosure deep beneath the temple which had once been an ancient Sith shrine that the Jedi had built over. After the Emperor dispatched Moff Wilhuff Tarkin and Darth Vader on a mission to the planet Murkhana, 11-4D reported that Tarkin had departed in his starship Carrion Spike. Sidious instructed the droid to alert him when the ship landed on Murkhana. Sidious subsequently returned to his meditation.
After the insurgent Berch Teller and his rebel cell stole the Carrion Spike, 11-4D was present at a meeting between Sidious and his Joint Chiefs including Admiral Conan Antonio Motti, General Cassio Tagge, Rear Admirals Kendal Ozzel and Tiaan Jerjerrod, COMPNOR Director Armand Isard, Imperial Security Bureau Deputy Director Harus Ison, Colonel Wullf Yularen, and Naval Intelligence Vice Admirals Dodd Rancit and Terrinald Screed.
During the meeting, 11-4D plugged one of its appendages into an interface socket that routed holofeeds to the summit from the former . 11-4D also complied with the Emperor's orders to tint the windows. The Emperor and Joint Chiefs witnessed footage of the Carrion Spike attacking the TaggeCo mining facilities on Lucazec. When the Emperor asked 11-4D if the droid puzzled out what was happening, 11-4D confirmed the affirmative and reported that the holovid was being transmitted by the Carrion Spike. In response, Sidious dispatched reinforcements to aid Tarkin and Vader, including one of the latter's black Eta-2 Actis-class light interceptors.
11-4D was later present when Sidious questioned the ISB case officer Stellan and the Koorivar informant Bracchia about the discovery of the communications cache on Murkhana which had led to the theft of the Carrion Spike. The two confirmed that they were acting on information which had been passed by Military Intelligence, of which Naval Intelligence was a branch of. Satisfied with their explanation, Sidious tasked 11-4D with checking the holovid sent by Military Intelligence to ISB. When 11-4D pointed out he could find no record of the holovid, Sidious said that the video was in the ISB's archives. After 11-4D retrieved the holovid, Sidious found that the holovid was a fake which had been created by someone with access to Imperial codes and to devices capable of subverting the HoloNet.
Vader and Tarkin subsequently discovered that Rancit was a traitor who was supplying intelligence and weapons to Teller and his insurgents in order to boost his own standing in the Imperial Ruling Council. While Vader executed Rancit, Tarkin defeated Teller's rebels during the Battle near the Gulf of Tatooine. The defeat of Teller's insurgency led to Tarkin's promotion to Grand Moff and allowed the Empire to continue with the construction of the first Death Star.
11-4D served Darth Plagueis and his successor Darth Sidious, and had apparently taken several guises throughout his time of service. The droid had many more arms than a typical protocol model, and only two of them terminated in hand-like appendages. The rest were devoted to tools of various purpose, such as computer interface and power charge extensions. 11-4D once oversaw the excavation and restoration of Sidious's private lair; an ancient Sith shrine underneath the deepest recesses of the Imperial Palace. The droid also served as Sidious' servant and assisted him with various duties including relaying holofeeds and retrieving holovids.
11-4D first appeared in the current Star Wars canon in the 2014 novel Tarkin, written by James Luceno. Before that, 11-4D originally appeared in the 2012 Star Wars Legends novel Darth Plagueis, also written by Luceno.
In 2012, during a question and answer session on Facebook, Luceno opined that 11-4D was there when Anakin Skywalker transformed into Darth Vader, depicted in a scene from 2005's Star Wars: Episode III Revenge of the Sith.