The first appearance of Krypto is as Superboy's pet in the early Silver Age. He was sent into space as a means of testing Jor-El's interstellar spacecraft before risking the life of his son, reflecting the similar use of animals to test rockets during the then-current Space Race. Arriving on Earth, Krypto became the playmate of Clark Kent (even receiving a "secret identity" as Skip, the Kent's farm dog.) After Superboy grew up and moved to Metropolis, Krypto was described as having gone off planet to "romp in space".
Krypto served as a member of both the Legion of Super-Pets and the Space Canine Patrol Agent s. During his time with the Legion he was impersonated by Proty II during the protoplasmic creature's petition for membership into the organization. Proty II returned from his super-task disguised as Krypto carrying the actual Kryptonite-exposed canine covered in protoplasm. Ever the loyal companion, Krypto died in battle with the Kryptonite Man to save his master during Alan Moore's story Whatever Happened to the Man of Tomorrow.
The first Post-Crisis Krypto was seen in the Time Trapper's pocket universe, as the former pet of that world's Superboy. Another Krypto was an ordinary Earth puppy adopted by Superman supporting character Bibbo Bibbowski, who had wanted to name the pup after Superman's home planet, but the engraver who made his dog tag was a "chis'ler" who tried to charge Bibbo extra for more than six letters. This dog was later given to the cloned Superboy, Kon-El, much to the chagrin of the Kid, who pawned off care of the boisterous puppy on friends and neighbors.
When Superman and Lois Lane traveled to a false planet Krypton on its final days, they found that the house they stayed at had another visitor. When they traveled back to Earth, Krypto followed. When exposed to the sun's rays, he showed the same powers as the Man of Steel himself. At Superman's wishes he stays at the Fortress of Solitude as a guard. As a result, Krypto was for some time locked away.
He made sporadic appearances over several years. He is used by Batman to sniff out the whereabouts of Poison Ivy during Hush. He is part of a rescue team, comprised of Nightwing, Superboy, Robin, Natasha Irons and Cir-El, that raids the White House to save Superman and Batman from President Luthor. He attacks the new Supergirl in the Fortress of Solitude.
Superman puts Krypto in Superboy's care and they settle down in Smallville. He came to Conner's aid when Superboy-Prime came to kill him, however, an injured Krypto was left behind in the heat of the battle, a battle that ends in Superboy's death. Krypto disappears soon after and when he makes his return, Superman allows Jimmy Olsen to keep him for a short time. During the Sinestro Corps War Krypto and Superboy-Prime have a brief rematch. He also comes to Superman's aid against Atlas, helping to defeat the magical threat. During the events of New Krypton, it is established that Krypto now lives on the Kent farm with Martha Kent after Jonathan Kent dies.
With Superboy's return, Krypto and Conner are once again reunited. When Superboy was turned into a Black Lantern, Krypto helped Connor to take control once more. He distracted Superboy long enough for Wonder Girl to fly to the Fortress of Solitude. Krypto followed, unburying Superboy's body. This confused the ring, which left the living Superboy to head towards his corpse. Superboy was then able to freeze it and throw it into space.
DC New 52
Krypto's origin was altered in the new 52. An experiment by Jor-el to create a companion for his son Krypto was implanted with some of the young Kal-El's DNA in order to create a companion with an unbreakable bond. In Krypton's final moments, Jor-El tries to save his family by opening a portal to the Phantom Zone nearly allowing the escape of its incarcerated prisoners. Krypto, aware of the danger they represent, leaps into action to defend his family and is subsequently trapped in the Phantom Zone. The young Kal-El is left in anguish at the loss of his dog. Later a homeless person tells Clark Kent that he is being watched by a ghost in the form of a white dog later revealed to be Krypto's projection from the Phantom Zone. After the escape of the Phantom King from the phantom Zone Kal-El was able to pull Krypto from the Phantom Zone. However, Krypto was severely injured. Worried, Kal-El carried Krypto into space, and threw him near the Sun, healing Krypto of his injuries.
As of recently, Krypto has been appearing around with Superboy. Krypto is different in the DC New 52 series. In the new version he is a wolfdog and he is Superboy friend and he helps him out in the Superboy's series to take a bite out of crime and help find Superman and family.
Superman: The Animated Series
Krypto briefly appears on Krypton in the first episode of the series when the planet is still peaceful.
Krypto the Superdog Tv Show
Krypto the Superdog is from Krypton and is sent to Earth for a test run. When he arrived at Earth he was full grown and had Super-powers. He got adopted by a boy name Kevin and his family. Krypto became a super-hero and only Kevin knew his identity. Kevin can talk to him with the help of a communicator, as can other animals. He teamed up with many other super animals, such as Ace the Bat-Hound and Streaky the Supercat.
A Red Setter is given super powers from an experiment with Kryptonite. Clark toys with naming the dog Krypto, but ultimately names the dog Shelby.
Batman: The Brave and the Bold
Batman and Krypto team up to take on Superman when he is briefly turned evil with a red kryptonite necklace. Together, they manage to keep the Man of Steel busy long enough for the Red Kryptonite to wear out.
Krypto appears briefly at the beginning of this movie and seems to have taken a dislike to Supergirl. Batman appears to agree with him.
DC Universe Online
Krypto appears as an NPC in DC Universe Online. When Brainic invades the Fortress Of Solitude, Krypto aids the player in the fight.
In 2006 a series called Heroclixs we see a dog Krypto in the series made and has powers and speed to fight in the game series. Krypto does not have a card with his appearance. That came until later in 2007. Krypto will be remade in the Heroclixs series and will have his card of his powers and comic book appearance.
Powers and Abilities
Krypto is smart for a dog but his intelligence is not on par with that of a human. He possesses a general understanding of speech, and can take direction well. He is also shown to be smart enough to understand most situations involving humans and can take initiative on his own to save the day when needed. He is also very protective of his family and can be ruthless against threats to it.
He possesses an even more keen sense of hearing and smell than Superman (as would be expected of a superdog) and his strength and speed is also proportionate (meaning he is faster but doesn't have the sheer strength of Superman). Due to Krypto's Kryptonian biology he also possesses many of Superman's other abilities, most notable his near physical invulnerability and the power to defy gravity.