Chieftain of the Bordermen, during Althurin's reign known as "King of the Bordermen", is one of the self-styled titles held by the head of House Blackgard, ruler of the bordermen and Lord of Ebonheart. The Chieftain of the Bordermen is effectively the ruler and leader of the bordermen race in general.
The title is reminiscent of a period in which the name "Bordermen" was applied to a small First Men tribe native to the Ashlands, living splintered and separate from each other, ruled independently by multiple chiefs. It wasn't until Asterion the Black unified the Bordermen under his rule that he became the sole chieftain of the bordermen.