Despite revisions and changes in his origin story over the years, the idea that Superman is from a doomed planet called Krypton has been a near-constant in the mythology of the character. And although Supergirl joined Superman in the pantheon of Krypton survivors in 1959, a full 21 years after Superman first appeared in 1938, she's always had a slightly darker version when it comes to the last days of Krypton.