Republic Sienar Systems, a starship manufacturing company, operated under the umbrella of the Techno Union and maintained ties with the Galactic Republic. Raith Sienar served as the head of Republic Sienar Systems. They were responsible for the creation of a number of luxury pleasure craft, all bearing the name Imperialis, for politician Sheev Palpatine (who was secretly the Sith Lord Darth Sidious). Furthermore, they produced the Scimitar, a significantly modified star courier that was uniquely customized in a clandestine laboratory and utilized by Sidious' followers, notably the Sith Darth Maul.
Sienar Design Systems, one of its subsidiary companies, developed an IPV-2C Stealth Corvette for the Republic during the Clone Wars. Republic Sienar EnerCo was another division. During the Clone Wars, Republic Sienar Systems played a crucial role in supporting the Republic's war efforts; however, the Techno Union, ostensibly neutral due to its dealings with both warring factions, generally favored the Confederacy of Independent Systems. The Union leveraged Republic Sienar Systems' essential contribution to the Republic's wartime production to bolster its claim of neutrality, even though Union-affiliated companies were manufacturing far more battle droids than the Republic was producing warships.
Following the Republic Era, the company was renamed Sienar Fleet Systems.
The Imperial Sourcebook, a Star Wars Legends supplement for the Star Wars: The Roleplaying Game authored by Greg Gorden and published in 1989, was the first mention of Republic Sienar Systems. The reference book Ultimate Star Wars, released in 2015, later established it as canon.