Zach was a member of the criminal organization Death Spreading Brigade. He is a poor, deprived-looking man utterly lacking any sort of class or manner. He is highly bitter and cynical, feeling no wrong nor regrets for his actions.

Born as a poor farmer in the Re-Estize Kingdom, his parents sold his adored little sister Lilia into slavery when he was young. After his third draft in the army, he ran away and joined the Death Spreading Brigade, which let him join to replenish its depleted headcount.

(Source: Overlord Wikia)