Gill

A human who roams in Victoria Island as a monster hunter. He is an extremely powerful swordsman, capable of outmatching both Gallus and Barrow. In actuality, Gill is a Dark Knight and utilizes the Beholder's powers, but uses a sword instead of the typical Spear or Pole Arm fit for such a class. As a monster hunter, he sees all monsters as his enemies and intends to slay them all so humanity can rise above them. Throughout the anime, Al asks that Gill joins him, but refuses, although Gill often shows up when a powerful monster appears and retreats when necessary.

(Source: Wikipedia)