The Ilari (sometimes referred to as the Ilarians) are a humanoid race native to the planet Ilari in the Delta Quadrant. By the 24th century, the Ilari were warp-capable and had a rigid form of government, which was headed by an Autarch.
In the 22nd century, the Autarch of Ilari was a warlord named Tieran. Tieran was a man who rose to power during a time of crisis and became a well respected leader, however in peacetime he proved to be a less reliable leader and soon became deeply paranoid and dangerous. He was eventually removed from power following a coup d'etat and was executed. However, Tieran had developed a way to transfer his consciousness to another host body and was able to survive.
Tieran eventually returned to Ilari while using the Ocampan female Kes as a host body and once again proclaimed himself Autarch after killing the current Autarch. Fortunately, the crew of the USS Voyager were able to remove Tieran's consciousness from Kes's body. Once Tieran's plans had been defeated, Demmas, the previous Autarch's eldest son, was named his successor. (VOY episode: "Warlord", VOY short story: "Winds of Change")