A Kilji individual known by the designation "Vassal Four" was a member of the Kilji species' governing body, the Kilji Illumine, functioning as a Kilji vassal who adhered to the Kilji religious beliefs. He held the position of comm operator on the Kilji war cruiser Whetstone, which was under the command of the Illumine's leader, Generalirius Nakirre. In approximately 18 BBY, while Nakirre was allied with the Grysk operative "Jixtus" and the Whetstone was stationed at the Unknown Regions planet Zyzek, Vassal Four informed the generalirius about a message being broadcast by the Chiss heavy cruiser Springhawk and proceeded to play it for him.
Subsequently, Vassal Four initiated a transmission with Chiss Patriarch Clarr'ivl'exow, also known as "Rivlex", acting on Jixtus' instructions. As the communication was being rerouted, the vassal voiced his objections to accepting the redirection, expressing concern that the indirect nature of the transmission might prevent Rivlex from responding. Despite this, Nakirre commanded Vassal Four to accept the redirection, compelling him to comply. Rivlex then answered the communication.
Vassal Four made his debut in the 2021 novel titled Thrawn Ascendancy: Lesser Evil, which serves as the concluding installment in the Star Wars: The Ascendancy Trilogy authored by Timothy Zahn.