A member of the Kilji species, known as "Vassal Four," was a Kilji vassal who served the Kilji Illumine, the government of the Kilji. As a follower of the Illumine's religious beliefs, he found himself in the role of a crewmember on the Kilji war cruiser Anvil, under the command of General Crofyp. In 18 BBY, Vassal Four worked at the warship's comm station. When Crofyp's task force, which included the Anvil and the Kilji picket cruiser Hammer, reached the Unknown Regions' Rapacc system to rescue refugees, they were confronted by the Nikardun blockade frigate Aelos, which was under the control of the Paccosh.
General Crofyp then gave Vassal Four the order to communicate with Colonel Tildnis, the commander of the Hammer. The order instructed Tildnis to navigate the picket cruiser along the portside of the frigate and proceed towards the planet Rapacc. After the Hammer had moved into position, the Chiss heavy cruiser Springhawk appeared in the system and destroyed the Anvil. The Hammer then escaped into hyperspace.
The character of Vassal Four made an appearance in Thrawn Ascendancy: Lesser Evil, a 2021 novel. This book served as the concluding installment of the Star Wars: The Ascendancy Trilogy, and it was authored by Timothy Zahn.