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Presenting Imperial Knight Masters Antares Draco, Sigel Dare and Ganner Krieg from STAR WARS Legacy of the Force.
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Imperial Knights are an order of Force Sensitive Jedi that served the Empire-in-Exile (Formerly known as the Fel Empire) - a long, long time ago after Luke Skywalker had become one with the Force. They were formerly known as the Knights of the Empire till Darth Krayt's One Sith Empire came to power and kicked them out.
They were founded because Jagged Fel - squeeze of
Jaina Solo - thought that it would really be great if the Imperial Remnant had Jedi Knights.
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In essence, Imperial Knights are trained Jedi who instead of being loyal to the ways of the Force, swear fealty to the Emperor of the Empire BUT with the clause "As long as he serves the Light Side of the Force." Because of this they were rejected by the Jedi Order and considered "Gray Jedi" - or Jedi who rejected the Dark Side of the Force but did whatever was necessary to bring "Order and Peace to the Galaxy" (Very Anakin Skywalker, but think of them a bunch of Qui Gon Jinns who "Do what they must" with or without the council's permission).
With the fall of the One Sith Empire and the rise of the Galactic Federation Triumvirate led by Admiral Gar Stazi, Jedi Master K'Kruhk and Imperial Knight and heir to the Fel Empire, Empress Marasiah Fel, the Imperial Knights remain separate from the Jedi Order, but now consider them allies - for now.