Krypto the Superdog

• Krypto the Superdog (voiced by Samuel Vincent) is the main protagonist of the show, formerly Superman's pet on Krypton before it was destroyed. Krypto came to Earth in a rocket when it malfunctioned. He is a white Labrador Retriever and has all of the powers of Superman, though some are heightened due to being a dog, such as his super hearing and sense of smell. Krypto also shares Superman's moral values and feelings.
• Streaky the Supercat (voiced by Brian Drummond), Krypto's best friend and sidekick, is an orange Somali cat with a yellow streak along his back who lives next door to Krypto and Kevin's family. He gained Kryptonian-like powers and weaknesses after an accident involving a duplicating ray that was aimed at Krypto, but deflected off him and hit Streaky instead. Unlike Krypto, Streaky is less serious about his superhero activities, and sometimes needs prodding to perform heroic deeds, but usually is dependable. He also has a nephew named Squeaky who is the leader of the Supercat Fan Club. Streaky often refers to Krypto as "K-Dog".
• Ace the Bat-Hound (voiced by Scott McNeil) is Batman's pet German Shepherd (though Ace says that he is Batman's partner) who is an ally of Krypto, Streaky and the Dog Star Patrol. Ace fights crime utilizing various detective skills and gadgetry built into his collar (an analogue of Batman's utility belt); he also uses a rocket sled for traveling long distances. Ace wears a dark-colored cape and collar similar to Batman's, and (like Batman) possesses a stoic personality. However, Ace does occasionally work alongside Krypto and considers him an ally. Ace's nemeses are Catwoman's pet cat, Isis, the Joker's two pet hyenas Bud and Lou, and the Penguin's three trained pet birds Artie, Griff, and Waddles.
• Kevin Whitney (voiced by Alberto Ghisi) is the 9-year-old young boy who Krypto lives with in the series, with Superman's permission. Kevin enjoys Krypto's company greatly, and is able to communicate with him and the other animals in the series thanks to a universal translator device. Kevin has a bratty cousin named Bailey who finds out Krypto's secret, but fortunately, he is such a notorious liar that no adult believes him.
• Andrea Sussman (voiced by Tabitha St. Germain) is Kevin's next-door neighbor and the owner of Streaky. Andrea enjoys making Streaky play dress-up, but was unaware of his (or Krypto's) superheroic identity until later in the series, when she accidentally stumbles upon Krypto's spaceship. In "Iguanikkah", it is revealed that Andrea is Jewish and celebrates Hanukkah. She loves to play and dress up Streaky, and she treats him like a baby.

The Dog Star Patrol are a superpowered group of canines who each possess a unique superpower, and fight crime across the galaxy. Krypto joined the Dog Star Patrol by helping the group out on a mission. Ace the Bat-Hound and Streaky the Supercat also helped them out on different occasions. The group is based on DC Comics' Space Canine Patrol Agents with elements of the Legion of Super-Heroes. Members of the Dog Star Patrol include:

• Brainy Barker (voiced by Ellen Kennedy) is a purple Saluki and leader of the Dog Star Patrol. Brainy Barker possesses telepathic/telekinetic powers, allowing her to read minds, project force fields, and levitate objects.
• Mammoth Mutt (voiced by Kelly Sheridan) is a pink Chihuahua with the ability to inflate her body to an enormous ball-shaped size, allowing her to use her size to attack foes. She can also expand other parts of her body.
• Bull Dog (voiced by Michael Dobson) is a lavender Bulldog with a stereotypical British accent and two retractable, bull-like horns that can be used for attacking foes and breaking objects.
• Paw Pooch (voiced by Dale Wilson) is a yellow and brown Basset Hound with eight legs that enable him to dig and run quickly. They can also grow in size, as seen in "Puss In Space Boots".
• Tail Terrier (voiced by Peter Kelamis) is a green Scottish Terrier with the ability to stretch his tail and use it like a lasso. He also has a stereotypical Texas accent.
• Tusky Husky (voiced by Terry Klassen) is a sky blue Siberian Husky with a stereotypical French-Canadian accent and a giant front tooth which is incredibly durable and can be used as a drill.
• Hot Dog (voiced by Trevor Devall) is a red Dachshund with the ability to generate tremendous heat from his body and breathe fire. He also has a short temper, but started to control his anger in "Bones Of Contention".
• Drooly (voiced by Ty Olsson) is an Old English Sheepdog who can use his drool as a weapon in various ways, such as grabbing objects, creating bubbles, and using it as projectiles. He appeared only in "The New Recruit" and was made a reserve member after defeating Mechanikat's forces.

• Superman (voiced by Michael Daingerfield): The main superhero of Metropolis and Krypto's original owner. He was only seen in "Krypto's Scrypto", allowing Kevin to watch over Krypto because of how busy he is.
• Stretch-O-Mutt (voiced by Lee Tockar): Buddy, a Bloodhound at S.T.A.R. Labs, accidentally fell into a vat of chemicals and developed shape-changing powers similar to Plastic Man and Elongated Man. Sometimes he can be too silly for his own good.
• Thundermutt (voiced by Phil Hayes) is an egotistical, world-famous canine actor who was somewhat jealous of Krypto when he "stole" the limelight at one of his movie premieres (Thundermutt II: Scratch And Sniff). Though he is cowardly, he is also mostly good at heart. The films he has appeared in, that are mentioned in the show, are Thundermutt II: Scratch And Sniff, Invasion of the Alien Cats, K-9 Krusader and Harry Rottweiler and the Doghouse of Doom (a parody of Indiana Jones and the Temple of Doom).
• Jimmy the Rat (voiced by Phil Hayes) is a rat and informant for Krypto and Ace.
• Robbie the Bird Wonder (voiced by David Paul Grove) is an American robin whose life was saved after he witnessed an encounter between Ace and the Joker's hyenas. After that, he decides to be Ace's sidekick, much to Ace's dismay. Robbie was based on Robin. Like Ace, he has gadgets like a glider, birdarangs, and egg bombs and he also came back to Gotham to be partners with Ace.
• The Supercat Fan Club is a group of kittens who are fans of Streaky, and occasionally assist him in crime-fighting despite not having powers. They consist of Streaky's nephew Squeaky (voiced by Lee Tockar), Nikki (voiced by Kathleen Barr), Puff (voiced by Samuel Vincent), and Ramone (voiced by Brian Drummond).
• Melanie Whitney (voiced by Tabitha St. Germain) is Kevin's 2-year-old baby sister. She knows that Krypto ("Kippo" as she puts it) is Superdog, but being a baby, her parents do not take her seriously.
• Smokey (voiced by Phil Hayes): A Dalmatian who appears in "Old Dog, New Tricks". He believes that the firemen are going to replace him with a new puppy. So Streaky paints spots on Krypto to prove that Smokey is still up to the job, though at the end of the episode, he is still in the Fire Service working with Blaze.
• Blaze: A Dalmatian puppy in "Old Dog, New Tricks". Streaky thought Blaze was intended to be Smokey's replacement, but Smokey explained that Blaze is his new trainee. The firemen believe that Smokey can teach Blaze the ropes until the time he helps in fire emergencies.
• Dooley (voiced by Brad Swaile) is a dolphin who befriends Krypto and Streaky when they were turned into fish in "Furry Fish".
• Dogbot (voiced by Scott McNeil) - a robot dog built by Jor-El to keep Krypto company while he was in space, he appears in the episode of the same name and "Dogbot To The Rescue".

• Mechanikat (voiced by Mark Oliver) is the main antagonist of the series and is based on Metallo. Mechanikat is a cyborg feline, who constantly plots to conquer Earth. He usually keeps a bit of green Kryptonite on hand to use against Krypto, or to power up his machines with so they can affect Krypto. He is also a member of the Intergalactic Villains Club (a spoof of the Legion of Doom) who gather in a base similar to the Hall of Doom. Due to Mechanicat's repeated failure to defeat Krypto, he has been unable to get elected as leader with the recent election having the members voting for Glorg to be the leader of the Intergalactic Villains Club.
• Snooky Wookums (voiced by Nicole Bouma) is Mechanikat's sidekick and secret agent. Snooky is a blue kitten mastermind who uses his cuteness and intelligence to cause trouble. He later became part of the Supercat Fan Club.
• Delilah (voiced by Kathleen Barr) is another feline agent of Mechanikat. She helped make the Katbots, and is skilled in kung fu.
• The Katbots are the foot soldiers of Mechanikat.
• Ignatius (voiced by Scott McNeil) is the pet green iguana of Superman's archenemy, Lex Luthor. Like Luthor, Ignatius is very intelligent, vain and is morally ambivalent, but he is effete, selfish and tends to behave in a much less dignified manner than Luthor. He is also more prone to engaging in frivolous (and dangerous) personal whims, such as employing a growth ray to enlarge a caterpillar for food or using a wind tunnel to harvest one of Krypto's hairs as part of a scheme to grow a lovely fur coat. Notable is that on occasion, he shows basic morals and honor.

• Lex Luthor (voiced by Brian Dobson): An evil genius and the owner of Ignatius, who is very intelligent and uses technology to take over the city. He is Superman's archnemesis that is always causing chaos and is the CEO of LexCorp where he makes his own top secret gadgets.
• Bud and Lou (voiced by Peter Kelamis and Lee Tockar): A pair of spotted hyenas who serve the Joker, previously having been created for Batman: The Animated Series. Their names are references to comedians Abbott and Costello. Additionally, they are depicted with red fur and are practically identical in appearance, only being distinguished by their collar colors - Bud purple and Lou green.
• Isis (voiced by Kathleen Barr) - Catwoman's cat, originally created for Batman: The Animated Series, who like her is seductive, a master thief and like how Catwoman often flirts with Batman, flirts with his dog Ace. In Batman: The Animated Series she was a black or dark gray cat - possibly a Russian Blue; here, she is a Siamese.
• The Bad News Birds - three trained birds who work with the Penguin and are usually up to some elaborate caper. They consist of the puffin Artie (voiced by Dale Wilson), vulture Griff (voiced by Matt Hill), and penguin Waddles (voiced by Terry Klassen),
• Dogwood (voiced by Louis Chirillo) - a half-dog, half-plant hybrid who can bring plants to life. He bears a striking resemblance to another cartoon canine, Muttley.
• Mertin the Magnificent (voiced by Scott McNeil) - a magician's rabbit who wields a magic wand that he stole from his master. His only real intentions are stealing carrots, but he can hold his own against Krypto and Ace if confronted by them. His name is a reference to the famous wizard, Merlin.
• Superflea (voiced by Scott McNeil) - a Kryptonian flea who stowed away on Krypto's ship. Like all Kryptonian creatures, it gained a multitude of powers under Earth's yellow sun. It was ultimately driven off by a spray can, and stowed away on a plane.
• The Junkyard Dogs is a group of never-do-well stray dogs. At best small-time hoods, they do periodically menace the heroes, and once took advantage of Krypto when he lost his memory due to Red Kryptonite. They consist of Mutsy (voiced by Lee Tockar), Beazel (voiced by Brian Drummond), and Beane (voiced by Samuel Vincent). Additionally, Rosie (voiced by Janyse Jaud) was formerly part of the group and Mutsy's girlfriend, but later left and was adopted by flower saleswoman Mrs. Fritch.
• Krypto's Tail (voiced by Samuel Vincent): Once, when Krypto was exposed to Red Kryptonite, his tail became sentient, separated from him and caused havoc in Metropolis. After Krypto and the Dog Star Patrol defeated it, they learned that it only wanted freedom, and brought it to an island to roam until the Kryptonite's effects wore off.
• Bailey Whitney (voiced by Reece Thompson in Season 1 and Noel Callahan in Season 2) is Kevin and Melanie's bratty cousin, who bullies Kevin and Krypto. Bailey too discovered Krypto's secret and has unsuccessfully tried to reveal it.
• Blackbeak (voiced by Brian Drummond): A thorn on Stretch-O-Mutt's side. Blackbeak is a parrot who leads a pirate crew called the Pi-Rats, who steal cheese and crackers. He additionally wears a Kryptonite necklace and hates cats.
• Barrump Barrump (voiced by Phil Hayes) is a sinister space monkey who pulls pranks all around the galaxy. In his self-titled episode, he steals a device that freezes time so that he can pull pranks on everyone on Earth. He is known as the "Primate Prankster" and is one of the galaxy's most dangerous criminals.