Power Girl's History
As originally created, Power Girl was Kara Zor-L, the cousin of the Superman of the parallel world of Earth-Two (and thus, she was her Earth's counterpart of Supergirl). When the Earth-Two universe's Krypton was about to explode, Kara's father Zor-L launched her as an infant to Earth in a ship at the same time that Kal-L's ship was launched; however, Kara's ship took a much longer journey, resulting in her arriving on Earth in the 1970s, decades after her cousin. Unlike Kal-L's ship, Zor-L constructed her ship (or "Symbioship", as it was called) to hold Kara in stasis through the longer journey. In addition, the ship's artificial intelligence carried the life experiences and education of a Kryptonian in the form of a virtual reality wherein she interacted with virtual copies of her parents and fellow Kryptonians. By the time she landed on Earth, Kara had aged into her early 20's (post-Crisis, as referenced in JSA Classified, her initial age has been revised to about eighteen).
Unlike her counterpart Supergirl, Power Girl's existence was not revealed to the general public until much later, as her cousin Clark and his wife Lois provided her a family environment to assist her transition towards real life relationships. Her first recorded case was assisting the Justice Society members Flash and Wildcat in containing an artificially induced volcano which had erupted in China. She then joined them and other younger heroes Robin and Star-Spangled Kid to form a Super Squad along with then active members of the Justice Society to defeat Brainwave and Per Degaton's scheme for world domination. She was later provided full membership when she took over the vacated spot on the team's roster left when Superman retired from active membership.
Having been raised by the Symbioship with artificial Kryptonian life experiences Power Girl had trouble fitting into life on Earth, but with the help of reporter Andrew Vinson, eventually adopted the secret identity of computer programmer Karen Starr. She obtained her knowledge in this field from treatment under Wonder Woman's purple ray on Paradise Island. She never wore a mask or other disguise between her two identities and, at some point, her identity was revealed to the public.
Power Girl's best friend was Huntress, Helena Wayne, the daughter of the Earth-2 Batman and Catwoman.
The 1985 limited series Crisis on Infinite Earths retroactively erased the existence of the Earth-Two Superman, and Power Girl's continuity was thus substantially disrupted. Following the series, her background was retconned; she became the descendant of the Atlantean sorcerer Arion, having been frozen in suspended animation for millennia until the present day.
In the late 1980s Power Girl joined the Justice League (the Justice Society having been disbanded in the interim). Later, while a member of Justice League Europe, she was badly injured by a mystical being. Superman assisted in her medical treatment, using his heat-vision to enable surgery to be performed on her otherwise-invulnerable tissues (without his intervention, Power Girl would have perished). Although she recovered, she was significantly weaker, lost all of her vision powers, and could not fly for a time.
Later, she mystically became pregnant and gave birth to a son (Equinox) during the Zero Hour crisis. Her son was subsequently artificially aged, became a superhero, and disappeared.
Power Girl was established as being the first partner for Oracle in what grew to become the Birds of Prey. The partnership ended when a mission failed disasterously, resulting in a large loss of life. Power Girl believes that bad orders from Oracle were to blame for the tragedy, and dislikes Oracle intensely as a result (although she has worked with her again on a few occasions when needed).
Power Girl's costume has varied significantly over the years. During her time with Justice League Europe/America it transitioned to a capeless yellow and white bodysuit, followed by a blue and white costume with a short mini-cape, headband, with a diamond shaped opening on her chest. In the late 1990s Power Girl's original costume design was restored: a white bodysuit, red cape, blue gloves and boots, with the presence of "round window" on her chest depending on the artist depicting her. In her guest appearance in Green Lantern, Kara is seen in her large wardrobe closet with every costume design she's ever worn in DC continuity, deciding which costume to wear for that mission.
During the miniseries that established her ancient Atlantean origin, Power Girl was portrayed with a highly athletic but slender physique. In the limited series Kingdom Come, artist Alex Ross restored Power Girl's extremely busty shape, rendering her as heavily muscled (as if an ardent bodybuilder). This approach has been carried forward by most other artists. The character's appearance and costume have become somewhat controversial, as Power Girl's voluptuous figure has been made light of in several recent appearances.
When the Justice Society re-formed in the late 1990s, Power Girl joined as a key member.
Power Girl's backstory as a descendant of Arion was called into question when Arion himself admitted that her origin as an Atlantean was a story that he had created for her own protection at her foster mother's request (the Lois Lane of Earth-Two).
The Psycho Pirate, the source of Kara's multiple origins in an effort to drive her insane, revealed to her that the Kryptonian origin was her true origin: Power Girl was a survivour of the Krypton of Earth-Two. It is still unclear why she survived the Crisis, even retaining her pre-Crisis origin, when other Earth-Two figures, such as the Huntress and Robin, did not. It seems likely that Power Girl's survival has something to do with the fact that the remaining relative from her old life was Kal-L, who was also still alive.
In the pages of Infinite Crisis, Kal-L himself returned to the post-Crisis DC Universe after breaking down the walls of the paradise dimension in which he, Lois Lane, Alexander Luthor, and Superboy-Prime had been living since the end of Crisis on Infinite Earths. Appalled by the rapidly-deteriorating state of affairs on the contemporary Earth, their goal was to replace the post-Crisis planet with a recreated Earth-Two. Kal-L tracked down Power Girl, explaining the events of the original Crisis to her. He also revealed her pre-Crisis history as his cousin. A touch from the ailing Lois Lane-Kent served to restore Power Girl's Earth-Two memories.
Soon after this revelation, she was confronted by Superboy-Prime, who rendered her unconscious. Power Girl was attached to a ?tuning fork,? a device controlled by Alex Luthor whose purpose was to bring back the multiple Earths. Alex Luthor and Psycho Pirate coerced Black Adam (also attached to the machine) into saying "SHAZAM!," and used the now-raw magical energy to power the tower. Initially, only Earth-Two was restored, and everyone associated with that Earth was transported to it. (However, Power Girl remained on Earth-One because of her proximity to the tower.)
The Lois Lane of Earth-Two died moments after her arrival there with Kal-L. This led to a violent confrontation between the two Supermen, at the end of which Kal-L came to the realization that Earth-Two had not been a perfect world since "a perfect earth doesn't need a Superman."
Kara was freed by Wonder Girl and Kon-El and joined them in fighting Superboy-Prime and Alex Luthor. Left on Earth during the savage battle on Mogo between Superboy-Prime and the Supermen Kal-L and Kal-El, she was brought to Mogo by the Green Lantern Corps just in time to bid a tearful farewell to her dying cousin.
A year afterwards, she has apparently recovered from her traumatic ordeal, and taken her place once again in the Justice Society of America. Interestingly, she has also become Nightwing in the city of Kandor, fighting a cult that worships Kal-El, with Kara Zor-El as her sidekick, Flamebird.
