September 22 is the Earth-equivalent birthday for Kara Zor-El, Superman's cousin better known to the world as Supergirl.
The subject of her own TV series launching next month, Kara Zor-El traveled to earth shortly behind her more famous cousin Kal-El, but was delayed in arriving and by the time she got here, he was fully-grown rather than the baby she expected to find.
While a "Super-Girl" first appeared a year earlier, Kara Zor-El's canonical first appearance was in 1959. Her history is long and complex; at one point, she died during the Crisis on Infinite Earths, but when the DC Universe was reborn following those events, she wasn't included. A new Supergirl -- who came from a pocket dimension and wasn't actually Kryptonian -- took over for a while, and then a post-Crisis version of Kara arrived years later.
Post-Flashpoint, Kara has become a key part of the Superman mythology. Meanwhile, her pre-Crisis counterpart seems likely to have cheated death when she, Barry Allen, the post-Crisis Superman and Hal Jordan/Parallax from Zero Hour all traveled back to the Crisis to battle the Anti-Monitor together. Both Superman and Parallax survived and made it back to the current DC Universe; that version of Superman will star in Superman: Lois and Clark starting in October, while Parallax will appear in Telos. The status of the pre-Crisis Kara and Barry Allen is unknown.
Interestingly, Kara shares a birthday with Laura Vandervoort, the actress who played her on Smallville.