Created by Geoff Johns, Courtney Whitmore is the stepdaughter of Pat Duggan aka Stripsy, the Star-Spangled Kid's adult sidekick. she becomes a hero after finding the Star-Spangled Kid's gear in his stepfather's belongirngs. To annoy her new stepfather, she becomes the new Star-Spangled Kid. In later adventures, Jack Knight aka Starman gives her his Cosmic Staff, which lead her to change her codename to Stargirl.
[Source: IGN]