Matrix(Supergirl (Pocket Universe), 1988-1996, 2000-2002)

In a Pocket Universe created by The Time Trapper, three Kryptonian criminals escaped the Phantom Zone and tried to take over Earth. This universe's only hero, Superboy, had died prior to the criminals' escape. This world's Lex Luthor created an artificial lifeform from a protoplasmic matrix. He patterned the creature after the deceased Lana Lang, and gave her powers that mimicked those of Superman, a hero in the primary universe. The girl, whom Lex called Matrix, was given a feminine version of Superman's uniform. Matrix fought the three villains, but she was no match for their combined might. Lex sent Matrix into the primary universe to recruit Superman. Superman did succeed in stopping the villains, but not before the Pocket Universe Earth had been obliterated. Superman took the orphaned Matrix back to the primary universe with him. Matrix was taken to live with Superman's parents, Jonathan and Martha Kent. They named her "Mae". Later, Mae met and fell in love with Lex Luthor. She assumed the name "Supergirl" and became Luthor's bodyguard. When she later learned that Luthor was using her, Supergirl went berserk and nearly killed him. Mae began to contemplate her life, and wondered if she was even a real person. When Matrix used her shapeshifting powers to try and save a mortally wounded Linda Danvers, the two women instead merged into one. Matrix and Linda formed a new Supergirl, with Matrix as the dominant personality. Matrix and Linda were later separated. Later still, Matrix merged with a superhuman named Twilight.