Mammon was one of the main antagonists of Before the Fall.
We first see Mammon in the Shiganshina District when the Titan Cult opens the gates for their "God". Because 3DM Gear hadn't been invented, Mammon saw little to no resistance, and thus ate his way thorough the districts, before returning to the wilderness. But not before vomiting up one of his victims, Elena Munsell, who already in labor. This miracle child would be known as Kuklo, or the "Titan Child".