On Krypton, parallel evolution led to the emergence of analogous species to Terran cats, simians, birds and dogs, which were domestic companion animals as they were on Earth. 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.^[1] 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.^[2] 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. Whenever he was on Earth and wanted to appear as an "ordinary" dog, Krypto would simply pull his collar and its attached cape off, pulling it back on when necessary. In one story, he was gifted with a collar which contained a retractable cape within the collar that could be unfurled or hidden by pressing a stud on the collar.

When not accompanying Superboy/Superman, Krypto spent much of his time romping through space; while on Earth, however, he stayed with the Kent family, posing as their pet dog, "Skip". In that identity, his guardians applied a brown dye patch on his back for a disguise which Krypto could burn off with his heat vision when he went into costume; later, the Kents devised a pullcord-activated dye applicator and other methods which Krypto could use to switch to "Skip" and back without assistance.^[3]

Krypto had the distinction of belonging to two organizations of super-animals: the 30th century Legion of Super-Pets, and the Space Canine Patrol Agents.^[4] After the 1971 revamp of Superman by editor Julius Schwartz, Krypto made no appearances for several years.^[5] The character returned suffering from amnesia in a two-part Green Arrow backup story in Action Comics #440^[6] and 441.^[7] His memory was restored in Superman #287.^[8]

Krypto had his own feature in The Superman Family #182 (March–April 1977) to #192 (November–December 1978) and it was written by Bob Toomey.^[9]

In the final (noncanonical) pre-Crisis Superman story, Alan Moore's Whatever Happened To The Man of Tomorrow?, Krypto sacrificed his life to save Superman by biting the throat out of the Kryptonite Man. The villain died but Krypto was irradiated by him and died as well.

In Superboy #126 (Jan. 1966) "Krypto's Family Tree", Krypto's father's name was given as Zypto, his grandfather as Nypto, and his great-grandfather as Vypto.

The modern Krypto[edit]

Pocket universe Krypto[edit]

Following the 1985-1986 Crisis on Infinite Earths limited series, Superman's history was extensively rewritten, initially eliminating all other survivors of Krypton in the revised version of his origin, including Krypto, so as to once again make the premise that Superman was truly the "Last Son of Krypton" a valid one.

Eventually Krypto in several forms was reintroduced to the Superman mythos, the first being as essentially an exact copy of the pre-crisis Krypto existing in a pocket universe created by the Time Trapper.^[10] In this early Post-Crisis storyline, Superman found himself in this pocket universe in which, similar to the Pre-Crisis Earth Prime of Superboy-Prime, his teenage counterpart was the only superhuman on Earth.^[10] Combatting the genocidal forces of the three Phantom Zone criminals, this alternate Superboy had an intelligent Krypto counterpart as well, who heroically sacrificed his powers for his master to provide him with gold kryptonite to defeat his enemy. This was the same pocket reality from which the "Matrix" Supergirl originated.

Krypto and Bibbo[edit]

The second modern Krypto was a small white pet dog, rescued, and later named by Bibbo Bibbowski. Originally, Bibbo had wanted to name the dog "Krypton" after Superman's home planet. However, the engraver of the dog tag (knowing that Bibbo had recently won the lottery) intentionally dropped the letter "n" ("Six letters or less for 1 dollar"), so he was trying to extort more money from Bibbo; an angry Bibbo refused to comply and renamed the dog "Krypto." Soon after, the dog found two young children who had been trapped in a bomb shelter for a month following Superman's fight with Doomsday. The children were badly malnourished and dehydrated, but it was learned that they would survive and recover. This gave Superman the idea to explain Clark Kent's long absence by staging a faked rescue from a similar predicament.

Krypto was later acquired by the modern Superboy; however, this version of Krypto was an ordinary Earth dog with no superpowers, and the dog and Kon-El didn't get along. For a time, Krypto's friends were agent Rex Leech, Rex's daughter Roxy, the being from the genetically engineered race at Cadmus called "DNAliens" known as Dubbilex, and TV reporter Tana Moon. Krypto became involved in many of Superboy's adventures. The dog was eventually dropped from the series, remaining in Hawaii when Superboy returned to Project Cadmus. Superboy's friends believed him to be missing and Krypto was left in the care of a neighbor that he liked, a young woman named Hillary.^[11] After Superboy #69 of that series, the dog went to live at Cadmus. Krypto, a creature called Grokk the Living Gargoyle, and a DNAlien named Angry Charlie, started an uprising against the Agenda, an evil consortium which was influencing Cadmus at the time. After battling a DNAlien named the Gene-gnome, Krypto was never seen again, his last appearance in Superboy #74.^[12]