Created from parts of numerous sewer-dwelling reptiles, as well as spare parts from abducted homeless citizens, Sewerstein was The Facility's last attempt at reptile hybridization.
They attempted to create a super-animal for military application, but the monster (nicknamed "Sewerstein" by the surgeons that created him) proved to be less than obedient... And was scheduled for termination. Unbeknownst to the Facility, he had become self-aware and independent and had escaped.
The Facility has taken special interest in retrieving Sewerstein but armed with his super-strength, super-durable hide, and his weaponized cybernetic arm, he will be difficult to reclaim. Since his escape they have turned to another species, to continue their quest in creating anthropomorphic super soldiers.