Demon King

The Demon King was the leader of the Demon King Army and the primary objective of the Hero Party's ten year quest. He waged war against the human kingdoms of the continent from his castle in Ende for thousands of years before being slain by Frieren and her comrades. Despite his importance in the world, relatively little is known about him so far. Though Demon are solitary creatures without human emotion, he commanded the loyalty of all Demon.

Personality
While not much is known about the Demon King's personality, while most Demon value individuality, the Demon King notably fostered order amongst Demon and was able to maintain loyalty amongst demonkind. Like Macht, the Demon King desired coexistence amongst humans and Demon. He was strongly devoted to this goal, to the point where he wiped out so many countries and people that he reduced mankind's sphere of influence by a third.

History
One thousand years before the era of the Hero Himmel the Demon King ordered his subordinates, including a general of his army and at least several extremely powerful demon mages, to massacre the elven population. Frieren's village was destroyed and its population killed, leaving her as the sole survivor of her village. Ironically, this led to Frieren meeting Flamme, who would go on to train Frieren and give her mission of killing the Demon King, which she succeeded at many centuries later.

Approximately twenty years before the Hero Party defeated him, the Demon King Army's offensive intensified, leading to a large increase in the number of mages in the overall human population. It was common to pass by mages walking through the streets of any regular town. However, by about twenty-nine years after Himmel's passing, mages had become a rare sight, only spotted in specific magical towns such as Außerst.

Following his defeat, nearly all his direct higher ranking subordinates disappeared without a trace. However, the remnants of the Demon King Army were still a significant threat to the human kingdoms, and almost a century after his defeat still constitute large enough forces to wage wars against human armies, and hold the northern part of the continent. Notable Demon of high status from the Demon King army to appear so far include Qual and Aura, both killed by Frieren.