Power Girl, also known by her birth name Kara Zor-L and by her human name Karen Starr, was the Pre-Crisis Earth-2 counterpart to Supergirl of Earth-1 (Kara Zor-El). Power Girl is cousin to Kal-L (The Golden Age Superman) from the planet Krypton 2, and like her Earth 1 counterpart, was sent to Earth after Krypton 2 exploded. During her journey through space, Power Girl had lived what she thought to have been a real life, but was later revealed to be a simulation while she lay in suspended animation along her journey. When Kara is found by Kal-L, he rejoices but keeps her a secret much longer than her counterparts. She would later live with Kal-L and his wife, Lois Kent. Kara then adopted the alias Karen Starr.
As Karen Starr, she has recently founded an engineering company devoted to helping the planet through the use of advanced technologies. The company is known as Starrware Labs.
Power Girl made her debut with the JSA.
On Earth-Tangent, a paralell world from the multiverse, there is a very different version of Power Girl, who is not Kryptonian but is nonetheless extremly powerful. She is the mate of the Tangent world's version of Superman.