Dr. Herman Frayne was the mastermind behind the plan to transform humans into amphibian-like creatures which he dubbed the "Hydro-Men." Herman Frayne also went by the alias Dr. Hydro. He was an ecologist who believed that man's only salvation was to adapt and live in the sea. The followers of Dr. Hydro built an artificial island off the Atlantic coast and used a chemical mist that mutated them into green-skinned scaly amphibians.
Dr. Hydro also used the chemical to hijack five airliners and to expose the passengers as well. Hydro originally planned on building an underwater city but later decided to invade Atlantis instead. Namor the Sub-Mariner came to the rescue of the humans and defeated the cult with Dr. Hydro meeting his apparent end. Hydro's test subjects were later returned to normal by Mister Fantastic.
Dr. Hydro later turned up alive and sought revenge for his defeat. He attempted to destroy Atlantis using the heat from a nearby volcanic crater. Namor investigated the situation and discovered Dr. Hydro's plot. Namor launched the Atlantean navy against Dr. Hydro's base and they destroy it. He then defeated Dr. Hydro and sealed his semi-solid form in a casket.
