In the original continuity, Cassie Sandsmark was the second hero to adopt the name "Wonder Girl", the first being Wonder Woman's sister Donna Troy. She was the daughter of Zeus and an achaeologist. After helping Wonder Woman fight not one but two supervillains using some magical artifacts, Zeus gave Cassie super powers as a reward for her bravery. Cassie would later join Young Justice before being promoted to leader of the new Teen Titans.
In her earlier appearances, Cassie was a plucky daredevil heroine who deeply admired Donna Troy. As she grew older and suffered one tragedy after another, Cassie gradually lost her confidence and her relationship with her teammates became strained.
In the New 52 universe, Cassie was originally a thief who collected rare magical artifacts. She was drafted into the Teen Titans by Red Robin, likely as a way of keeping young super-humans from causing too much damage. She also hates being called Wonder Girl.
In Other MediaWonder Girl appeared in the animated series Young Justice.
Like her best friend Batgirl, she is a very tough girl, she joined the Young Justice crew during the invasion. She and Batgirl battled Lobo on New Year's Day 2016. She and her mentor, Wonder Woman were part of the Delta Squad. She was also one of the team members, past and present. She joins the team to welcome the Justice League back to Earth. She worked alongside Robin. In the series finale of the show, she and Tim allowed Static to the team and she and Tim became an offical couple.
SuperboyCassie developed a crush on Superboy shortly after meeting him. When Superboy died, Cassie's normally fiery personality was eclipsed by depression. She joined a superhero-worshipping cult in the hopes of resurrecting Superboy, only to be talked out of it by a fellow superhero who had lost a loved one. Cassie continued to become increasingly withdrawn, which caused tension among her fellow Titans. Eventually Superboy was resurrected and after coming to terms with this, Cassie rekindled her relationship with him.
Red RobinTim and Cassie started out as just friends, but after Superboy's death, both were left in a fragile state. Tim tried cloning Superboy, but because he was already a clone of Superman, the procedure was a failure. Cassie gave Tim a shoulder to cry on and they wound up kissing. When Superboy comes back, Tim and Cassie keep their distance.
In the New 52 universe, Superboy and Wonder Girl were never in love and most of her intereactions are with Red Robin, hinting at a possible romance. Tim and Cassie have even shared a few kisses, though this is yet to be elaborated on.
- The New 52 version of Cassie's character bears some resemblance to Catwoman. Both are master thieves, both are initially neutral characters before becoming more heroic and both strike up a relationship with a non-super-powered detective (Batman/Red Robin)
- In the original continuity, Wonder Girl was dating Superboy. In the New 52 continuity, Wonder Woman is dating Superman, one of the few instances where the older generation of superheroes inherits the younger generation's customs.
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