Star Wars Knights of the Old Republic II: The Sith Lords is a role-playing video game developed by Obsidian Entertainment and published by LucasArts. It is the sequel to BioWare's Star Wars: Knights of the Old Republic and was released for the Xbox on December 6, 2004, for Microsoft Windows on February 8, 2005, and for OS X and Linux on July 21, 2015. Like its predecessor, it is set in the Star Wars universe 4,000 years before the events of the film Episode I: The Phantom Menace and is based on the d20 System developed by Wizards of the Coast. The game uses the Odyssey Engine, which was originally used in Knights of the Old Republic. The plot first started being written before the original Knights of the Old Republic was released, and development began in October 2003, after BioWare offere