For the VOY episode of the same name, please see "Warlord".
A warlord was an individual who has assumed control over an area through armed force.
During the 22nd century, warlords existed on Preenos. (ENT: "Oasis")
A warlord existed on Kelis' homeworld in the late 24th century. (VOY: "Muse")
In 2374, Major Kira Nerys called the Female Changeling an "intergalactic warlord" and claimed that she was trying to turn Odo into one. (DS9: "Behind the Lines")
In the years preceding 2399, the Qiris sector became overrun by petty warlords, including Kar Kantar, who along with smugglers called the shots in the region. (PIC: "Absolute Candor")
Given the name of the episode in which Ilari former Autarch Tieran appeared, he can most likely also be considered a warlord.