13 years ago - Krypto is born in Suicide Slums in Metropolis.
11 years ago - 2-year-old Krypto is saved from being frozen by Clark Kent & taken to the Fortress of Solitude to heal. The Eradicator rewrites his DNA to make him a Kryptonian creature. After he has changed back, he exhibits some kryptonian biological traits, and must stay in The Fortress.
10 years ago - 3-year-old Krypto helps Clark Kent battle General Zod in The Fortress when he escapes the Phantom Zone.
3 years ago - 10-year-old Krypto goes to live with Connor Kent in Smallville, and befriends Kara Zor-EL.
1 year ago - 12-year-old Krypto helps in the fight against Maggeddon.
It's really easy to make fun of the idea of Superman's super-pet. It's a goofy holdover from the Silver Age: Otto Binder made Captain Marvel one of the best-selling characters of the era with a wide supporting cast, and he set about doing the same thing with Superman's cast. He had already created Supergirl when for some reason he swerved into animals. Krypto was followed by Streaky the cat, Comet the horse, Beppo the monkey... It just got weird. This was one of the parts of the pre-crisis DC that we're all better off without.
Still, even after the timeline reset, we just kept getting new versions of Krypto. Pocket universes, time-warped Brainiac constructs, or just normal dogs befriending his supporting cast, Krypto came back over and over. .
We happen to think there's a very specific reason for it. There are very few things more wholesome than the relationship between a person and their dog, and seeing a character bond with a dog immediately makes you feel a kinship with that character. For a character like Superman having us trust and like him is paramount, and depicting his relationship with Krypto really helps convey that. Showing Krypto's complete trust in Connor Kent even made him a more sympathetic character.
All that said, there's still a central difficulty with incorporating Krypto into our story. Not just the usual question of "How did ANOTHER Kryptonian character survive the destruction of Krypton?". This time you also get "Krypton has dogs? really?"
Obviously, Krypton has PEOPLE, so the idea that they have dogs isn't completely insane, but it's still a weird pill to swallow. We decided to actually make Krypto a normal old earth dog that was rewritten with Kryptonian DNA by the Eradicator. Frankly, the superpowers are the least important part about him, they just make him adorable. Those big trusting labrador eyes are what make him great.