While everyone knows the names of Superman and Supergirl, Superwoman is a unique moniker held by multiple superpowered women over the years of the DC Universe. One of the more memorable women to hold the mantle of Superwoman is Lucy Lane, the younger sister of famed Daily Planet reporter, Lois Lane.
Before becoming Superwoman, Lucy Lane had taken up the job of a flight attendant, until a rogue terrorist hijacking attack left her doused in chemicals. However, these chemicals left her blind rather than with any special abilities. Contact with Bizarro, however, somehow inverted the process, restoring Lucy's eyes and giving her a new lease on life. So what led her down the path to villainy, and to become Superwoman?
Lucy Lane, before becoming Superwoman, was already well on her way to becoming some sort of supervillain. While it seemed for awhile she was on the path to rebuilding her life, with getting married and having a kid, she left it all to join the military, though not for the best of reasons. Lucy blamed both her sister and Superman for the death of her father, Sam Lane, who died during the "Imperiex War". Of course, it turned out General Sam Lane had not only survived his apparent death, but gone on to experiment with Kryptonian genetics in secret.
He had set out on a secret government war, known as Project 7734, against the Kryptonians living on the restored Bottled City of Kandor, now known as New Krypton. Lucy joined Project 7734, eager to eradicate the Kryptonians and Superman. One of the byproducts of these experiments was a suit, revealed in Supergirl Vol 5 #40 - 41 by Sterling Gates, Fernando Dagnino, and Raul Fernandez, granted Lucy the powers of a Kryptonian but none of the weaknesses. The suit was a creation of Mirabai the Forlorn, a tyrant sorcerer from Zerox -- the Sorcerer's World. Lucy Lane infiltrated New Krypton as Superwoman, posing as a liaison from Earth. However, along the way, Lucy just happened to commit a few murders -- most notably killing, Benjamin Lockwood, aka Agent Liberty, who had been investigating Project 7734. Eventually, Superwoman's secret reign of terror, working alongside her father to eradicate the "threat" of New Krypton, came to a head.
The event "Who is Superwoman," which ran from Supergirl Vol 5 #37 - 41 by Sterling Gates, Helen Slater, and Jamal Igle, featured Lucy Lane as the enigmatic Superwoman, committing violent acts of murder and destruction, all while Supergirl tried to figure out her identity. When Supergirl eventually realized Lucy was Superwoman, the two engaged in a fight. The fight came to a head when Supergirl, pummeling Lucy to the ground, declares that Superman is unworthy to wear the House of El's emblem on her chest. When she rips it off, however, it creates a chain impact in Mirabai's enchantments into the suit. The whole thing blows up, seemingly killing Lucy Lane.
Of course, Lucy wasn't all dead. She was restored to life, this time with the powers of her suit infused with her genetics. She kidnapped Lois during the events of the "War of the Supermen", the culmination of the "New Krypton" arc. Superwoman takes her to Sam Lane to watch as the general's sprawling plot came to a climax. Supergirl ultimately beat up Lucy Lane and brought her to STAR Labs. To ensure she'd never harm anyone again, Kimiyo Hoshi -- the good Dr. Light -- returned Lucy's genetic composition to how it had been before her experimentation, eradicating her powers.
Lucy's story ended tragically since the events had burned all the bridges she had with her remaining family, leaving her ultimately defeated, unable to ever truly recover from this event. However, the name "Superwoman" would go onto more deserving heroes who merited the title. Lana Lang and Lois Lane would later take up the mantle after absorbing the energy of the New 52's Superman as he laid dying. While Lois would eventually die and merge with her alternate reality counterpart, Lana would live on, though she would lose her abilities when the Pre-"Flashpoint" Superman reabsorbed his powers.