Ultima

Ultima was one of the Demons summoned by Diablo to serve Rimuru. He was Arch Demon when summoned, but evolved to Demon Duke after he was named.

Dispatched to Gabil corps as an intelligence officer

Personality
Rimuru think Maybe the one with the cruelest personality among three Demon Dukes might be Ultima

Trivia

 * He was named after sports car manufacturer Ultima Sports Ltd.