The Terrible Thunderlizards

Doc Tari or "Doc" (voiced by Savage Steve Holland), is the leader of the Thunderlizards team. He is a Parasaurolophus only with a hole in the center of his crest that contains many gadgets such as a buzz-saw and a grappling hook. More often than not, he is the team's most focused member, but is every bit as unfocused as Kutter and Squatt when not chasing the humans or performing missions. Doc, both in voice and mannerisms is a parody of various Arnold Schwarzenegger film characters such as John Matrix from Commando, Dutch from Predator, and with a bit of the Terminator. His catch phrase is "We move!".

Day Z. Kutter or "Kutter" (voiced by Bill Kopp), is the second-in-command of the team. He is a Styracosaurus, although he was mis-addressed as a Triceratops. As his name suggests, he is good with knives, being the master of the knife fight, and wears a skull T-shirt. Kutter is smarter than Squatt, but less intelligent than Doc. He is often shown fooling around with Squatt and at times requires Doc's quick wit and strength to help him focus.

Bo Diddley Squatt or "Squatt" (voiced by Jason Priestley in 1994-1996, Corey Feldman in 1996-1997), is the third member of the team and their top sniper. He is an Allosaurus. He is the typical "dim-witted clumsy screw-up" character, although in some instances he has been fairly competent. His voice and mannerisms appear to be similar to Private Hudson, Bill Paxton's character from the film Aliens. Squatt is often used as the volunteer to assess dangerous situations. His catchphrase involves asking if a particular event would qualify as a "bad thing", to which Kutter or occasionally Doc would respond, "Yes Squatt, that would fit nicely into the bad things category!".

General Galapagos

General Galapagos (voiced by Kurtwood Smith) is the boss of the Thunderlizards. He is a green bad-tempered Tyrannosaurus with a fat belly and a huge bottom. He wears a Blue General military uniform with a gold starred blue cap. When humans were starting to become a threat, General Galapagos had Doc, Squatt, and Kutter's prison sentenced commuted so that they can deal with the humans. He oversees the missions of the Terrible Thunderlizards to hunt down the humans but is continually frustrated that they never accomplish their mission. He was the one who foresaw that, given the trio's overall performance, their race is doomed.

Dr. Steggy is a Stegosaurus scientist (voiced by Charlie Adler) who works for the Jurassic City Military. He has a nephew called Huckleberry (voiced by Cam Clarke) who befriends the humans, Bill and Scooter.

Mr. T-Rex is Galapagos's best soldier. He is a Tyrannosaurus who is based on and voiced by Mr. T. Mr. T-Rex is a parody of Mr. T's characters Clubber Lang from Rocky III & B. A. Baracus from The A-Team, even using some of Mr. T's popular catch phrases. His anger frequently gets him into trouble resulting in the Thunderlizards having to save him.

Nate the Dragon (voiced by Nathan Wang) is a Velociraptor who is a stealth and martial arts expert using uses a Bo staff.

El Gordo is an unusually small Ceratosaurus who is an expert in camouflage and can disappear by sticking a plant in his hat.

Bill and Scooter are the two humans - Homo sapiens, called "mankinds" - the Thunderlizards struggle to eliminate so they will never evolve into the humans of today. Both Bill and Scooter wear animal skins (blue for Bill and red for Scooter) somewhat like the ones worn by male characters in The Flintstones, but only covering their right shoulders, and walk in animal skin shoes. While both are aware that the Thunderlizards are trying to kill them, they have no idea why or the anti-human prejudice from Dinosaur City. In a few episodes the pair befriend some dinosaurs such as Huckleberry.

Bill (voiced by Charles Adler) is tall and thin with red hair and is Scooter's ill-tempered partner. He is often used to test drive Scooter's devices often with chaotic, disastrous and painful consequences. Throughout the series, he uses the catch phrase "When does the hurting stop?", usually after one of Scooter's failed and painful experiments. Bill is continually depressed, sometimes almost to the point of psychosis. He has a love/hate relationship with Scooter; while he has been civil towards him at times and even occasionally protects him, he often gets driven to attempt to kill him after suffering some painful mishap from one of his inventions. While most of the time the pain Bill goes through is the cause of Scooter, more often than not Bill's misfortune comes from his own stupidity and stubbornness and refusal to listen to him. Bill is the target of choice for a particular species of jungle slug that regularly tries to eat him, though it has targeted Scooter on one occasion, as well.

Scooter (voiced by Curtis Armstrong) is short, fat and bald with a yellow beard. He is a jolly, overly enthusiastic caveman and inventor and is blissfully unaware of Bill's irritable attitude toward him. He is an eternal optimist seeking world peace and harmony and rarely panics unless being pursued by the Thunderlizards or when Bill attempts to hurt him. His inventions often fail and result in disastrous consequences where Bill is usually the victim. However, sometimes his inventions save him and Bill from being hurt by the Thunderlizards or other dangers in the jungle. Unlike Bill, Scooter is willing to find new ways to live and survive in the X-Zone and invent new things, and has developed somewhat of a bond with Babs over their love of inventing, most clearly shown in The Yawn of Man.

Babs is the first female human and was created by dinosaur scientists using recovered genetic material from Bill and Scooter spliced together, then doubling the X-chromosome to create a female. Her name comes from the acronym for Bio-engineered Animated Biped Specimen (BABS) and she believes strongly in "womankind". The Thunderlizards' goal was to use Babs to entrap the two men for the dinosaurs, but she was more intelligent than them and abandoned her original mission to live alone in the jungle. Babs is aloof and manipulative and was initially repulsed by Scooter and preferred the company of Bill who was easier to manipulate. Babs makes occasional future appearances where she comes up with ideas on how to use Bill and Scooter to further her aspirations.

The Thuggosaurs are a race of undead Grim Reaper-like dinosaurs that live in the X-Zone on the outskirts of Jurassic City which is a frequent target of the Thuggosaurs who are recurring antagonists in the program. The Thuggosaurs are a parody of the hooded, mutant survivors living in the Forbidden Zone from the movies "Beneath the Planet of the Apes" and prequel "Battle for the Planet of the Apes" in their targeting of Ape City. Thuggo (voiced by Brad Garrett in most appearances, understudied by Kurtwood Smith in four episodes) is the diabolical leader of a group of black-hooded skeleton-like Thuggosaurs. He is a Megalosaurus. His vanity insists he always look good, so Thuggo often spends more time trying to improve his appearance than accomplishing his evil plans - plans that would mean the end of the Living Dinosaurs once carried out. The Thuggosaurs sometimes have conspiracies that initially appear effective against the dinosaurs, such as kidnapping the president's daughter. Biff is Thuggo's wimpy, flower-loving, second-in-command and is inappropriate to be part of a villainous organization like The Thuggosaurs. Thuggo has an roundish skull-shape with sharp teeth-like bones while Biff has a long snout with bucky teeth and wears a pair of goggles. All other Thuggosaurs share similar features.

The primates are a group of simians who co-exist in the X-Zone like Bill and Scooter whom they regard as backward and primitive. They are more advanced than the humans, living in condominiums and with an advanced social structure.