Overview
Supergirl (also known as Cir-El or Mia) is a fictional superhero appearing in American comic books published by DC Comics. The character is best known as one of the characters to have assumed the mantle of Supergirl. Created by writer Steven Seagle and artist Scott McDaniel, she first appeared in Superman: The 10¢ Adventure #1 (2003) as the alleged daughter of Superman. She is later found to be a human girl who was genetically altered by the villain Brainiac to appear Kryptonian. The character dies thwarting a plot involving Brainiac 13. Superman (vol. 2) #200 implies that when the timeline realigned itself, Cir-El was erased from existence.
Fictional character biography
Superman: The 10¢ Adventure
When a crazed villain named Radion attacks Metropolis, a young girl in a costume leaps into battle and throws the villain into a nuclear reactor (in front of a TV news crew and Lois Lane). The girl identifies later herself as Supergirl, Superman's daughter. Upset, Lois confronts Superman, accusing him of having an affair (even listing Wonder Woman and Zatanna as possible lovers), and refusing to believe his claim of innocence, since "Supergirl" looks just like him. However, after a cup of the new "Yes" coffee, Lois suddenly calms down and dismisses "Supergirl" as a villain's hoax, until she lands in front of Lois and calls her "Mommy". Superman confronts the girl, who argues that she is his daughter with Lois, and that her name is "Cir-El". Cir-El says that she is from the future, brought to the past by the Futuresmiths. When Superman encounters the Futuresmiths, they show him a horrific future, with robotic monsters attacking civilians, and he sees himself as a cybernetic Superman attacking civilians as well. The Futuresmiths tell him that Cir-El's death will prevent this future, and as they turn to attack her, Superman flies her to safety. S.T.A.R. Labs confirms that she is his daughter, but that Lois is not her mother. Regardless of her identity, Superman comes to regard Cir-El as family.
Cir-El helps Superman fight off a diseased Bizarro. Later, with the aid of Natasha Irons and Girl 13, she fights off a vengeance-crazed superhuman ninja who is trying to kill Superman. When Superman and Batman are said to be "captured" by President Lex Luthor in Superman/Batman "Public Enemies", Cir-El teams up with Superboy, Krypto, Natasha Irons, and the Batman Family to rescue them.
From Wikipedia (CC BY-SA 4.0).