Introducing Krypto the Thunder Dog of Earth-Two

58 days before the destruction of Krypton-One, its leading scientist Jor-El used his family's pet as a test subject for his experimental  prototype rocketship. After orbiting the world below, the vessel was struck by a stray meteor, causing its engine to engage. After a month and a half of circling around the planet, Krypto's ship was pulled along through the spacewarp created by his young master Kal-El's rocketship, just as Krypton exploded.

Eventually, the puppy grew into a full grown dog, trapped within the vessel yet preserved alive thanks to yellow sun radiation which gave it super-abilities. Crashing on Earth-One years later, Krypto was finally freed from the ship and sought out his master, no longer a toddler but Superboy. As the Boy of Steel trained the Dog of Steel how to use its new powers with the help of the canine's increased intellect, Superboy enlisted Krypto's help in several adventures. In his civilian identity as Clark Kent, Superboy disguised Krypto and gave him a new alter ego as his dog Skip. After several years together, Krypto left to journey through space, although years later reunited with Kal... who was now Superman... on Earth-One. Krypto tried to romantically draw his master and Lois Lane together, to become husband and wife with him as their dutiful pet. Sadly, his scheme didn't succeed.

On Krypto-Two, Jor-L had less time to devise a test rocketship, and so sent his son Kal-L in an untested rocketship. Like his counterpart, Kal-L arrived on his new home world successfully. He grew up as Clark Kent and, in his teen years, as the Masked Wonder. While an occasional kind pooch would aid the now adult Clark in his Superman adventurers, Kal-L had no time to welcome one into his home until he gained a family of his own. Clark eventually married his coworker Lois Lane. 

Decades later, the Kents invited a new member into their family unit, although this dog was artificially constructed on Earth. That dog traveled to another world... that of Telos... with Clark, Lois and the city of Metropolis. The cyborg canine was named Thor who appeared to have found his new master after his former owner, Superman’s former All-Star Squadron teammate the Manhunter, had retired from superheroics. How he came to acquire Thor from the retired police officer Dan “Manhunter” Richards, whose grandfather Marcie Cooper became a friend then foe of a younger generation of superheroes on this world, has thus far been untold.

Krypto had at least one and perhaps other robot duplicates built by his master, as Superboy had done with himself as well. On Earth-Two, Thor the Thunder Dog had been built by the alien Manhunters when he was assigned to his first master Dan Richard in his crimefighting crusade of as the original Manhunter. Dan and Thor joined the Freedom Fighters who traveled to Earth-Two, with both returning to their home world in the late 40s. 

In an alternate future timeline, Thor was still Dan’s pet when he attacked his master under the control of the vengeful Manhunters who were still active in that future. Other cybernetic dogs like Thor were also built by the Manhunter androids, one of whom was assigned to agent Paul Kirk, who declined accepting it. In the mainstream future of Earth-Two, Thor remained a docile animal companion to the Man of Steel.

Both Krypto and Thor possessed superstength and speed beyond that of canines of their Earths. Additionally, each had enhanced vision and hearing along with other senses, with each apparently powered by solar radiation from Krypto’s Kryptonian genetics and Thor’s Manhunter cybernetics. While Thor was durable due to his metallic frame, he wasn’t invulnerable as was Krypto although Thor was immune to all radiation while Krypto was susceptible to Kryptonite radiation as that emitted by his arch-foe, Kryptonite Kid’s irradiated dog.