Cassandra "Cassie" Sandsmark, a.k.a. Wonder Girl, is a fictional character, a DC Comics superheroine. Created by John Byrne, and first appearing in Wonder Woman (vol. 2) #105 (January 1996), she is the half-human daughter of Zeus.
Young Justice was disbanded after the events of Graduation Day, a crossover with Titans. During these events, Optitron offered to fund both the Titans and Young Justice. Donna Troy was killed by a rogue Superman android, leaving Cassandra shaken and causing both teams to disband.
Cassandra later joined some former members of Young Justice in the newest incarnation of the Teen Titans. Early on, she was gifted with a lasso by Ares, the Greek god of war and frequent enemy of Wonder Woman and the Amazons. Despite appearing similar to Wonder Woman's lasso, Cassandra's expels Zeus' lightning when used in anger. Over the course of the series, Ares often appeared to Wonder Girl to warn her about "the coming war." During her time with the Titans, Cassandra also developed a relationship with Superboy, whom she had harbored feelings through before and throughout Young Justice.
In "Titans Tomorrow," the Titans are thrown ten years into their future, where they encountered the future versions of themselves. In this future, Cassandra inherited the mantle of Wonder Woman after Diana was killed during "the Crisis." She is also referred to as "Ares' champion," and is in a relationship to Conner Kent (Superman). It is not revealed whether they are formally married or still dating.
It was also during her Titans membership that she was revealed to be Zeus' daughter, a fact both Zeus and her mother kept from her for most of her life. Cassandra was originally told by her mother that her biological father died. Wonder Woman knew about Cassandra's link to Zeus but chose to hide this from Cassandra as well at the request of Cassandra's mother. In "The Insiders", she was beaten by Superboy as a result of his possession by Lex Luthor; though she recovered, Superboy secluded himself at the Kent farm in Smallville, and there had seemed to be a strain on their relationship until the events of Infinite Crisis.
During a battle against Brother Blood and a handful of zombie Titans, she acknowledged that her powers were fluctuating and sometimes disappearing altogether. Despite this, Cassandra attempted to help Superboy after he was beaten to near-death by Superboy-Prime After saving him, Cassandra and the Titans infiltrated a LexCorp laboratory to find a way to cure Superboy. While the other Titans flew to Blüdhaven following an attack from the Society, Cassandra remained at Titans Tower to watch over Superboy. When he awoke, the pair of them reconnected and remembered their past in Young Justice, which seemed so much happier and easier. Conner then took Cassandra to Smallville, and, afraid that it would be their last night together, had sex in the Kent barn.
Ares again appears to her and informed that the reason behind her weakening power was Zeus taking back the powers he had granted to her as he left the mortal plane. Ares then offered Cassandra some of his power in exchange for becoming his champion and acknowledging him as her brother. She joins Superboy and Nightwing up north, with powers returned, to assist in the assault on Alexander Luthor's tower. Superboy sacrificed his life to defeat Superboy-Prime and destroy the tower, and died in Cassandra's arms.
About five days later, Cassandra and her fellow cult members meet with Ralph. Cassandra mentions that it was another member, Dev-Em, who led her to join. Cassandra explains that the goal of the cult is to resurrect Superboy. As a test of their process, they intend to resurrect Sue Dibny. Cassandra and Ralph attend a ceremony designed to resurrect Sue, but Ralph grows suspicious and with the help of other superheroes, disrupts the ceremony, destroying the Kryptonite which was essential to the process. Cassandra leaves with Dev-Em, blaming Ralph for destroying her chances to resurrect Superboy. After stopping Weather Wizard in Metropolis, Cassandra meets Supernova and refers to him incorrectly as Kon-El, who actually turns out to be Booster Gold in disguise.
She temporarily rejoins the team, under the suggestion of Cyborg so that they may combine forces to defeat the Brotherhood of Evil. After the Teen Titans and Doom Patrol defeat the Brotherhood of Evil, she decides to rejoin the team permanently. When she goes to tell Robin of her decision, she discovers his secretive and unsuccessful attempts to bring back Superboy. Though obsessed with having Connor back, Cassandra reacts in horror and in an attempt to quell Robin's anger at Cassandra, the two kiss. For a while the two refused to talk about the incident beyond coming to the agreement that it was a mistake, but they both have discussed it with others. With her life in disarray, Cassandra has been having difficulty with her personal life, often having major confrontations with her mother. Cassandra has gained a new friendship with the recently returned Supergirl, Kara Zor-El, who has shared with her in mourning the loss of Superboy and Paradise Island.
Cassandra was also still very furious at Wonder Woman following the events of Infinite Crisis, due to Cassandra's belief that Wonder Woman abandoned her after Connor's death, to play secret agent in a new civilian identity that Batman created for her after Infinite Crisis. She was also not pleased that Robin was aware of Diana's whereabouts during the year after Infinite Crisis and didn't inform Cassandra about it. Diana and Cassandra have not been able to discuss their past differences, leading to Cassandra to turn to Supergirl and the now resurrected Donna Troy instead for emotional support dealing with Connor's death.
Following the resurrection of Jericho at the hands of Raven, Cassandra and Tim request that Raven use the same ceremony to resurrect Superboy. Raven calmly explains that isn't possible, because Jericho's resurrection was a special circumstance scenerio where Jericho's soul was still on Earth, imprisoned inside of a computer disk, while Conner's has moved onto to the afterlife. In the middle of this conversation with Robin and Raven, Cassandra is captured by Deathstroke's villainous Titans East after an attack by Inertia and Match. Each member of Titans East has been recruited to negate a specific Titan. Deathstroke selected Match, a Bizarro-type clone of Superboy, to counter Cassandra due to his strength and his warped visage as being a psychological edge against Cassandra.
The Titans battle furiously against the Titans East, during which they are able to convince Batgirl and Duela Dent to switch sides. Unfortunately the team is defeated by Slade's team a second time,. However, Raven, Cyborg, and Duela Dent manage to get aid from Nightwing, Donna Troy, Beast Boy, and Flash (Bart Allen). Together the Titans defeat Slade, who along with Inertia, manages to escape. During the fight Jericho possess Match, and the team is reluctant to release Match due to the danger he poses.
Cassandra then becomes involved in the Amazon’s attack on Washington D.C., Supergirl and Cassandra discover that their friends and family have been placed in an internment camp due to their ties to the Amazons. After a failed attempt to aid them, the two heroes agree to bring the U.S. President to Queen Hippolyta in order to stop the war. They are ambushed by a group of Amazons in the process, which causes the President to become mortally wounded. The actions of the Amazons and Wonder Girl's own involvement, causes public outcry against all those who have followed in Wonder Woman’s footsteps. At the end of the series, Wonder Girl and Robin share another kiss.
In the months following the kiss, Cassie and Tim continue to go through 'will-they-won't-they' moments in which they both continue to question the validity of their relationship. Then following a battle against an army of Future Titans, the pair decided at last to date. Unfortunately, their relationship is short lived, as after their first official date, Cassie ends the relationship, because she feels she is using Tim. This has resulted in a growing animosity between the pair, which has begun to bleed into their relationships with the other Titans.
Together, Hercules and Cassie try to discover who is attacking the remaining Olympian gods. Soon into their search they are attacked by the Female Furies. Hercules stops the fight by explaining that he's allied with the Furies in hopes of rescuing the gods, or, failing that, starting a new pantheon with them. The Furies have their own plans and are only using Hercules to get to Cassandra. The Furies soon betray Hercules, with Bloody Mary using her bite to gain power over Hercules, forcing him to do what the Furies want. The Furies then kidnap Cassandra's mother to lure her into a trap. Aided by the Olympian, Cassandra goes into battle, being forced to fight her own brother. The Teen Titans, Empress, Arrowette and Wonder Woman show up to help. After Bloody Mary is murdered by the New Gods killer, Hercules is freed from her spell and immediately saves Cassandra from being kidnapped by the Furies. Hercules goes free after he reveals he is now a demi-god and that Zeus released him to help stop "the Great Disaster". Hercules then leaves to perform certain "labors."
The series ends with Cassandra reconciling with Wonder Woman, who tells her that she has become her own woman.
She made a brief appearance in issue #55, sucker-punching Cyborg in his dreams.
Shortly after joining the Teen Titans, Ares approached her and gave Cassandra her own magic lasso. Unlike Wonder Woman's Lasso of Truth, Cassandra's is a weapon which channels Zeus' lightning. When the Greek gods left the mortal plane as a result of the events of Infinite Crisis, taking Cassandra's powers along with them, Ares offered her some of his power, saying that she would be "more powerful than [she's] ever been". What this entails is not made entirely clear, though she appeared to have retained all of her former abilities. In a storyline taking place "One Year Later", Cassie was shown catching a falling jet, which she was surprised at being able to accomplish. However, while trying to stop the military from detaining her mother, Ares causes her powers to fluctuate when he believes she is wasting them on frivolous matters.