Who, me? I'm not in trouble. And by the way, it's Supergirl. See? [points her chest] Super...girl. [points at her face]
~ Supergirl to Superman in "Little Girl Lost"
Supergirl was the last Argoan and Superman's foster cousin. She is a supporting protagonist in Superman: The Animated Series and Justice League Unlimited. She is voiced by Nicholle Tom.
Kara In-Ze was the only survivor from Krypton's sister planet, Argo. While exploring the sector of space once occupied by Krypton, Superman discovered a hidden cryogenic facility that had sustained heavy damage. Only one chamber was intact, containing the last survivor of Argo: Kara. Taking the young woman back to Earth, Superman introduced Kara to his adoptive parents. The Kent's took her in for three years, isolated from the world at large under Clark's instructions, in the guise of Jonathan Kent's teenaged niece.
Eventually, inspired by her "cousin" Clark, Kara made a costume similar to Superman's and occasionally joined on missions as Supergirl. Kara frequently visited Clark in Metropolis and, as Supergirl, she had full access to Superman's Fortress of Solitude. In Supergirl, Superman found a living link to his alien heritage, and someone he could talk to about his dual lives as Superman and Clark Kent. She became a frequent friendly ally who could be trusted with Superman's secret.
Before joining the Justice League, Kara had little interaction with other heroes. Her first official team-up was with Batgirl. When Livewire teamed up with Poison Ivy and Harley Quinn, Batman, asking for Superman's help, inadvertently gets Kara instead. Together Batgirl and Supergirl defeated the trio of super-villains and formed a close friendship. The two stayed close friends; a few years later, Barbara and Kara went skiing together for Christmas.
When Superman went missing, Kara took to the Fortress of Solitude to dispatch his robots to convince the world that he was still around. When Superman returned to Earth under Darkseid's control, Supergirl stood against him but was defeated. She was placed under the care of Professor Emil Hamilton, something that would come back to bite her in subsequent years.
Supergirl is a kind, sweet, and compassionate girl who loves to help people and fit in with others. Supergirl looks up to her cousin, Superman, and tries her best to protect him and help him protect the world from all kinds of threats.