Kagi was a captain who served Darth Sidious, the Sith Lord, after Sidious declared himself the Galactic Emperor of the Galactic Empire following his proclamation. After his duel against Yoda, a Jedi Master, in the Galactic Senate Chamber, Sidious instructed Mas Amedda to tell Kagi to ready his Theta-class T-2c shuttle for an immediate flight to Mustafar, a planet located in the Outer Rim. There, his new Sith apprentice, Darth Vader, was in a lightsaber_duel with Obi-Wan Kenobi, a Jedi Master.
The character of Kagi was initially referenced in the prequel trilogy movie Star Wars: Episode III Revenge of the Sith, which came out in 2005.