Villains
Cameron Winter (voiced by David Newsom) – A former classmate of Nick in college. He is a devious technological mogul whose desire is to control Godzilla for the furtherance of his ulterior goals. Smug and sadistic, Winter frequently taunts Nick and H.E.A.T. and often enacts various plans to keep Godzilla in line. He also knows how to cover up his acts and maintain his position, allowing him to avoid prosecution. At the end of the episode "Lizard Season," Winter has successfully sold his technology over to the US military and hides to build new robots to destroy Godzilla.
Dale, Bill, and Hank (voiced by Ronny Cox, Tom Kenny, and Bob Joles respectively) – Three big-game hunters who came to New York to hunt Godzilla. The three of them would usually try to hunt Godzilla which usually ends with them either being thwarted by H.E.A.T. or ending up arrested. Their names are a parody of three of the main characters from King of the Hill and their bumbling antics are comparable to The Three Stooges, of which they are even called as such by Winter.
Sidney Walker (voiced by Steve Susskind) - An electric bus maintenance worker who was undergoing a Theta wave therapy to cure his insomnia, but ended up in a coma-like state that eventually manifested his subconscious rage as the giant monster Crackler.
The Leviathan Aliens (voiced by Ron Perlman) – An ancient species of psychically powerful extraterrestrials. One of their spaceships, called the Leviathan, crashed on Earth sometime during the Cretaceous Period of the Mesozoic Era and remained hidden until modern times. In the three-part episode "Monster Wars", they attempt to conquer Earth by using a tachyon transmitter to send mind-controlling signals to subdue the mutations in order for their alien race to invade the planet - including Godzilla and their cyborg mutation Cyber-Godzilla (created from the carcass of the first Godzilla) - but are ultimately defeated by H.E.A.T and a freed Godzilla and forced to retreat.
Dr. Alexander Preloran (voiced by Kenneth Mars) - A brilliant xenobiologist who Craven idolizes. Preloran and his colleagues enter a sunken Leviathan ship, where Preloran decides to help them conquer Earth, believing it will help the planet. Preloran apparently sacrifices himself by launching an escape pod manually so H.E.A.T. and his colleagues can escape, though it is implied that he may have survived.
Dr. Hugh Trevor (voiced by Roddy McDowall) - A scientist who was studying Nessie the Loch Ness Monster, but wants to destroy it for attacking his lab. It is later revealed he kidnapped Nessie's baby and plans to sell it on the black market. Trevor attempts to escape with the baby in his submersible, but is thwarted by Nessie.
Dr. Jonathan Insley (voiced by Nick Jameson) - Insley is the creator of the D.R.A.G.M.A.s. In an alternate future, his creations had not only killed Godzilla, but also all of the other mutations on Monster Island, creating an apocalyptic scenario where humanity is forced to hide underground.
Maximilian Spiel (voiced by Clancy Brown) - A wealthy businessman and illegal fight promoter who also sets up a monster fighting tournament on a private island for other wealthy attendees.
Alexandra Springer (voiced by Linda Blair) - Alexandra Springer is the main antagonist in the episode "S.C.A.L.E." She is the fanatical leader of S.C.A.L.E. (short for Servants of Creatures Arriving Late to Earth), a radical animal-rights group that believe that mutations are the next stage of evolution and must be protected.
Tobias Wilson (voiced by Dorian Harewood) - A ringmaster of the mutant circus "Mutant Mania", he put a bounty on Godzilla, but Nick and H.E.A.T. saved Godzilla from the bounty hunters. Later, Nick confronts him for his bounty on Godzilla, telling Wilson to leave Godzilla alone or he'd do everything in his power to shut down Mutant Mania. When Medusa, a mutated sea anemone escapes and starts wreaking havoc in New York, Wilson tries to stop Mayor Ebert from destroying Medusa on the claim of "private property," but the mayor refuses. Wilson attempts to flee with Medusa, but is captured by the military.
Colonel Charles Tarrington (voiced by Michael Chiklis) - A US Army colonel who is heading a project overseeing the creation of mutant scorpions for weapons. After the first scorpion proves uncontrollable, he has a group of smaller, more controllable scorpions created. Having a high disregard for Godzilla and other mutations, Tarrington appears to see the error of his ways after Godzilla destroys the scorpions, but orders a new batch of scorpions created immediately after.
Paul Dimanche (voiced by Jesse Corti) - A corrupt business owner who was overfishing a Louisiana bayou and leaving the locals hungry. He begins flirting with Audrey when she interviews him over alleged abuse of over-fishing and illegal dumping into the swamps, of which he denied at first. He showed no care or concern for the safety of his guests when the Swamp Beast attacks his boat and mansion during Mardi Gras. After he was saved by Georges, he confessed to committing bribery which was unknowingly to him filmed by Animal. He is arrested afterwards.
Milo Sanders (voiced by Stuart Pankin) - An obnoxious and reckless tour guide of "Monster Liner", he bothers Nick and H.E.A.T. and ends up putting his passengers in danger while Godzilla was fighting the Deep Dweller. He also invited some photographers who attempted to get pictures of Godzilla up close, but were attacked by the Deep Dweller and had to be saved by H.E.A.T. However, while on deck, he discovers a video tapes that documents the location of Godzilla's lair and his bond with Nick and plans to reveal it to the public. Luckily, Animal called the news station and Milo's theft of the H.E.A.T. copter makes the news and leads to Milo getting arrested.
