Berserker

The Servant of Illya, he is a swarthy giant with adamantine skin and gross brawn. He wields a colossal stone Axe-Sword, and is capable of causing massive destruction with the mere backlash of his swings. As a Berserker, he was stripped of his sanity and reason, acting feral and animalistic in combat. Berserkers are praised as members of the "Strongest" class, though they are difficult to control. Illya, however, appears to have little trouble managing Berserker.

His real identity is Heracles (Hercules), the half-god and half-human hero from Greek myths.

(Source: Wikipedia)