Mezul

"“Those are foolish words only capable of coming from a Gozu, the ones working under Rimuru-sama will be we, the Mezu! You can vanish into seclusion and live a life without regrets!”"

- Mezurl Guardian of the 50 floor.

Background
He originally wish to form an alliance with Rimuru as the Mezu Representative, in order to form an alliance to massacre the Gozu, the Mezu's sworn enemy for the last 100 years. Rimuru immediately had an idea that he should place Mezurl inside the labyrinth as a boss unit.