Cassandra "Cassie" Sandsmark first appeared in Wonder Woman v2 105 as the obnoxious precocious daughter of Helena Sandsmark, curator at Gateway City's museum. During Diana's battle with a Doomsday clone, Cassie "borrowed" the Sandals of Hermes and the Gauntlet of Atlas from under Diana's bed (who normally keeps her gifts from the Gods in such places), which gave her super-strength, semi-invulnerability, and flight. This of course was all John Byrne's idea, as was creating a retcon that Diana's short hair in issues 90-100 was a wig. Cassie took the wig too, and using a pair of goggles to hold it on, went out to fight as the new fashion victim known as Wonder Girl.

In Wonder Woman v2 122, having been summoned to Mount Olympus by the Gods, Cassie requested a boon from Zeus. asking him to give her super-powers of her own. Zeus was so impressed by the girl's courage that he granted Cassie powers much like Diana's. The powers came with one drawback: her mother had the ability to cancel out her powers.

Initially Cassie wasn't sure what was worse: living under her mother's watchful eye or training under Artemis. She soon learned that jealousy was even worse than those could be.

As a member of Young Justice, Cassie was getting attention and recognition around the world as a new super heroine. Julia Kapatelis' daughter Vanessa had her anger and jealousy preyed upon and became the second Silver Swan. Vanessa attacked Cassie at her high school exposing her identity to the world.

After her secret was gone and she built a new life, she wanted to know her father. Understandably, she questioned why Zeus would grant a mortal powers so easily. She confronted him and asked if he was her father. While he lied and got away with it at the time, the truth always wins out in the end. At least in comic books.

After Donna was killed in Graduation Day, Cassie joined the latest version of the Teen Titans that had been gathered by Cyborg, Starfire, and Beast Boy.

It was during this time where Cassie learned that Zeus really was her father and was given a "gift" from her half-brother Ares of a magic lasso. Instead of compelling people to tell the truth, it channels Zeus' lightning.

Cassie became romantically involved with Superboy while with the Teen Titans. During the first annual, as Cassie was dealing with the loss of her powers during the Infinite Crisis, it looked as if Cassie and Connor were leaving Kid Flash as the only team virgin.

Ares appeared to her before leaving the Earthly plane with the rest of the Gods and empowered Cassie himself, claiming it was with no strings attached.

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After Superboy's death in the Infinite Crisis and the resulting one year leap forward in time, Cassie had left the Teen Titans and was known for relentlessly hunting down criminals. She returned to the team and now seems to be there to watch the Terminator's daughter, Ravager.