When did Supergirl first appear in comics, and what is her origin story?

Supergirl, whose real name is Kara Zor-El, first appeared in Action Comics no. 252 in May 1959. In that comic, following the explosion of the planet Krypton, Supergirl’s entire hometown of Argo City was hurled to safety on a chunk of planetary debris. Soon, however, the populace of the floating city began to suffer from exposure to Kryptonite, a radioactive mineral that sickens and debilitates Kryptonians. Faced with impending doom, Kara’s father, Zor-El—brother of Superman’s biological father, Jor-El—rocketed his daughter to Earth to join her cousin.

Kara Zor-El’s origin has been tweaked over the years. The 2004 relaunch of the character, for instance, introduced the idea that she had been sent to Earth to protect her cousin and that she had stayed in suspended animation during the trip.