Dr. Polidorius is a mad scientist obsessed with fish and wanted to sink the city so his fish mutants could inhabit it.
Polidorius operated in a scientific laboratory inside the Unbridled Technology building. Using his Evolution Accelerator, he created Ray and had him plant explosives in certain parts of the sewers so that he can sink the city beneath the ocean. Ray is just one of the first fish-men that Polidorius planned on creating for his underwater city. Ray kidnapped April O'Neil and Polidorius mutated her into a fish-woman in an effort to provide a mate for Ray. The Turtles tracked down Polidorius with the help of April's fish powers. The Turtles made him change her back to a human again, while Ray escaped into the ocean.
Polidorius never makes another appearance in the series.