Read more about Krypto at: Wikipedia
Official Site: D.C Comics
Krypto, also known as Krypto the Superdog, is a fictional character. He is Superman's pet dog in the various Superman comic book published by DC Comics. Krypto's first appearance was in a Superboy story in Adventure Comics #210 in March 1955.
As explained in his first appearance, Krypto was originally the toddler Kal-El's dog while they were on Krypton. Jor-El, testing prototypes for the rocket that would eventually send Kal-El to Earth, decided to use Krypto as a test subject. However, Krypto's rocket was knocked off-course; the rocket drifted through space for years until it eventually landed on Earth, where Krypto was reunited with the now-teenaged superhero, Superboy.
Due to the environment (Earth's yellow sun and lower gravity), Krypto possessed the same powers and abilities as his master, although his physical abilities were proportionate to his smaller size and species, similar to an ordinary dog vs. a human. Certain sensory abilities of Krypto's (senses of smell and hearing) would be more acute than those of Superman, just as an ordinary dog's senses would be more acute than those of an ordinary human. Krypto also had super-canine intelligence (approximately human level, though with his canine traits and interests still present); the comics expressed this via the use of thought balloons indicating what Krypto was thinking.
Krypto was drawn as a white dog of generic pedigree. The early appearances of the character in the comics usually featured exaggerated anthropomorphic facial expressions; these were replaced in later appearances by a more generic canine face. When fighting crime, Krypto usually wore a gold collar, a miniature facsimile of the famed Superman-"S" symbol for a dog tag, and a dog-sized version of Superman's cape.