Krypto

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 recieving a "secret identity" as Skip, the Kents' farm dog.)

After Superboy grew up and moved to Metropolis, Krypto was described as having gone off planet to "romp in space".

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 boistrous 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