Eulerex

Eulerex is a supporting antagonist character in How NOT to Summon a Demon Lord (also known as Isekai Maou to Shoukan Shoujo no Dorei Majutsu).

He is a powerful Fallen (a type of demonic/angel-like being) and serves as the leader of the so-called "moderate" faction among the Fallen. He has a cold, calculating personality, remains composed in any situation, and prioritizes the complete destruction of the races (humans, elves, etc.) above all else. He's strategic, ruthless, and willing to eliminate anyone — even fellow Fallen or a weakened Demon Lord — if they interfere with his goals or seem too "soft" on war and annihilation.

In the story (particularly in season 1 and related light novel arcs), he appears as an enemy who clashes with the protagonists, including attacking the revived Demon Lord Krebskulm (Klem) out of disappointment in her peaceful demeanor, only to be repelled by Diablo and others. He has an owl-like appearance in his true form and a humanoid one with owl features.

He's voiced by Kenji Kitamura in Japanese (and Andy Mullins in some English dubs).