Cassandra never knew her birth parents and was adopted and raised as the daughter of Corona's Captain of the Guards. She is an extremely skilled fighter who, throughout the series, has shown off her strength and prowess—defeating Wreck and Lance Strongbow easily. She dreams of joining the royal guard, though she currently serves as Rapunzel's lady-in-waiting and closest confidante, alongside the princess' pet chameleon Pascal. Her role generally requires that she assist Rapunzel in any means necessary while also being a constant bodyguard. She is also tasked with chores of a typical castle servant, such as maintenance.
Cassandra is described as being "tough-as-nails", a fitting description for someone who wishes to join the royal guard. She is snarky, sarcastic and has a somewhat dry sense of humor. She is also very intelligent, often subtly insulting Eugene in clever ways that go over his head. Despite this, she is extremely supportive and protective toward Rapunzel, her polar opposite—so much so, that she openly holds animosity for Eugene, believing him to be a selfish freeloader and undeserving of Rapunzel's love and friendship. In the series, however, their relationship gradually becomes less hostile, and slightly more playful as the two spend more time together. In "Fitzherbert P.I.", Cassandra genuinely admired Eugene's determination to become a royal guard, and actively assisted him in proving his worth to her father. It was later shown that Eugene's quirkiness had started to warm up to Cassandra, who found amusement in his excitement to school the guards as head of a training class.
Aside from her no-nonsense persona, Cassandra is also a free-spirit, not unlike Rapunzel. Though she has a more cynical way of going about life, Cassandra also finds joy in adventure, living life to the fullest, and experiencing new things. This is most notably seen during "Wind in My Hair", where Cassandra is seen enjoying herself almost as much as Rapunzel.
Although loyal to King Frederic and Queen Arianna, Cassandra is willing to break their rules (and risk her job) for the sake of Rapunzel's happiness and to accomplish her own dreams; this is seen when Cassandra offered to take Rapunzel beyond the kingdom's wall to explore some of the outside world and escape the pressures of royalty. Doing so required much stealth and cunning, traits Cassandra revealed herself to have abundantly that night.
In "Challenge of the Brave", it is revealed that Cassandra has some insecurities about how she is seen just as a girl/handmaiden instead of the strong, skilled, and capable warrior who deserves as much respect as anyone in the royal guard. These insecurities, and the desire to prove herself can sometimes drive Cassandra to act selfishly, even to those she cares about. Once she realizes her mistakes, however, Cassandra is mature enough to own up to her faults and make amends as best she can. Cassandra's cynical nature gives her trust issues. Examples are that she doesn't forgive people easily, she doesn't like sharing her feelings, keeps secrets to herself, or she won't accept help. This is one of the reasons she has a rivalry with Eugene because he was a thief in the past and she thinks he's ignorant enough to not address other people's feelings (even though it's not his fault he can't tell).
In "Not in the Mood", her personality develops a bit. She likes to show no mercy toward not just Eugene, but other suspicious looking people. She later realizes she should be more compassionate. For starters, she made friends with a man who was large and scary, but friendly.
She still has a firm belief that strangers can’t be trusted, especially when they lurk in the shadows. She jumps to conclusions about people’s actions rather quickly. If she doesn’t like someone, she’ll fight them. She even fights just for the fun of it, not in the mood for being nice.
Cassandra is a pale-skinned young woman with dark pink lips, hazel eyes and black bob-cut layered hair with gray highlights.
Her signature outfit is a grayish-brown shirt, black leather gloves, a dark brown belt with a purse and a dagger on it, dark brown-and-red striped leggings and brown boots.
When performing her duties as Rapunzel's handmaiden, Cassandra dresses in a blue and white dress, with a white headdress.
Since attempting to touch Rapunzel while she was reciting the Moonstone incantation, Cassandra's right hand and wrist were turned pitch black. To cover for her injuries, Cassandra donned a knight's armor and a purple cape.
When she is corrupted by the Moonstone opal, her hair and eyes turn turquoise and her clothes turn black and dark blue with spikes similar to the Black Rocks. The Moonstone opal itself becomes embedded in her chest.
Cassandra possess skills in horseback ridding, fencing, archery, athletics, and other skills in combat; which she had learned for being the daughter of the Captain of the Guards. She is also shown to be very clever when she understood Rapunzel's clues, had helped Varian with his project and spotting the mistakes in letters from a suspicious character. As well as possessing skills in acting, as she had tricked a Separatist of Saporia member into thinking that she has feelings for him, so he would come to Corona and she could uncover his true intentions. Cassandra also has skills in sewing, cleaning and others skills that are needed for her handmaiden duties.
After bonding with the Moonstone's power, she, most likely, receives the life-draining power that it possesses, as evidenced by its energy coursing through her hair.
Cassandra is first seen waiting for Rapunzel's return from a ride with Eugene at Corona's village gates. From there, Cassandra takes Rapunzel to attend to the various duties of a princess, specifically in preparation for her upcoming coronation ceremony to officially crown her as heir to the throne. Rapunzel laments her feelings of stress of the pressures of royalty overwhelm her. Cassandra believes the princess should take a break regardless of what her father wishes, but Rapunzel refuses to do so. Later at a dinner event, Cassandra sits with Pascal, while Rapunzel sits with her parents, and Eugene sits at the children's table (an arrangement made by Cassandra, who was in charge of seating). Eugene takes the time to propose to Rapunzel, but due to her fears of being bound to life in the castle, Rapunzel rejects and leaves. Seeing the princess upset angers Cassandra, who glares at Eugene.
That night, Rapunzel agrees to relieve her built-up tension by following Cassandra beyond Corona's border wall to explore the outside world for the night. Cassandra gears up for the adventure, providing Rapunzel with a hooded cloak and the two sneak their way out through a hidden passageway. They journey through the night forest, until Cassandra takes Rapunzel to a specific spot where the golden flower that saved Queen Arianna and the yet-to-be-born Rapunzel was grown. Suddenly, a blast of magic hits the two that causes Rapunzel's magic, golden hair to return.
The two return to the castle where Cassandra tries desperately to cut the hair. Like the rocks, it's unbreakable. When Eugene arrives, an anxious Cassandra urges Rapunzel not to tell him about the hair, fearing he'll tell the king and queen, which would cost Cassandra her job. He discovers regardless, but the three agree to keep it a secret from everyone else, including Rapunzel's parents. What Eugene still doesn't know, however, is how the hair came to be again. Cassandra refuses to tell him, and when confronted about her behavior towards him, Eugene discovers that his unintentional selfishness in regards to Rapunzel is partially to blame.
At Rapunzel's coronation, the hair is kept hidden beneath a wig, only to be revealed when she needs to utilize it as a weapon to fight off a band of thieves. While Rapunzel and Eugene fight off the goons, Cassandra takes on their leader Lady Caine. Caine is defeated and arrested for her crimes, though Rapunzel is reprimanded by King Frederic for the hair but Cassandra's part in restoring it was left out by Rapunzel.
In the premiere episode, "What the Hair?!", a week has passed since the return of Rapunzel's hair, and Cassandra is dead set on ensuring her involvement remains a secret. Rapunzel feels increasingly guilty over keeping Eugene in the dark, but Cassandra reminds her that if the secret is revealed, she would lose her job and be sent to a convent as punishment. After Cassandra subsequently proves Eugene's inability to keep a secret, Rapunzel agrees, though not without apprehension. By the end of the day, Rapunzel finally reveals the truth to Eugene, though he promises to keep it between them for Cassandra's sake.
Meanwhile, Cassandra deals with issues of her own, particularly pertaining to her goal of becoming a guard, which proves to be difficult due to both her father's overprotective nature and the reception she receives from the public (who evidently viewed Cassandra as a mere servant girl, incapable of anything more). In "Challenge of the Brave", Cassandra enters a challenge that tests the strength of its competitors to determine who is the mightiest warrior in all the seven kingdoms. She is shown as increasingly strong and capable, even sacrificing her win in the end to save Rapunzel and single handedly take down the last competitor. Though technically she loses in the end to Rapunzel, she nevertheless earns praise for her strength and exceptional fighting skills. Later in "Great Expotations", the guard is low on staff due to the kingdom's science fair, forcing the Captain to entrust Cassandra with filling in for the day, on the condition that she finishes her chores first. Varian asks Cassandra to act as his assistant during his presentation, and she agrees in exchange for having Varian handle her chores. This allows her to take on guard duty, but after being assigned to guard the esteemed Dr. St. Croix, Cassandra abandons Varian during his presentation. As a result of not having a reliable assistant, Varian is disqualified. Cassandra apologizes for her selfish behavior and offers her help when the experiments of the fair nearly destroy the castle. Proud of her actions, the Captain offers Cassandra another assignment as part of the guard, though she denies in favor of helping Varian clean up the mess.
Despite things ending on good terms, Cassandra was not satisfied with her performance at the science fair. In "Under Raps", Cassandra discovered — what she believed to be — a potential villain with interest in an ancient journal that originally belonged to one of Corona's previous kings. Cassandra sees this as an opportunity to prove her competence to her father and invites the mysterious foreigner (named Andrew), to see the journal while it is open to the public. By manipulating him into believing she was in love with him, Cassandra discovers that Andrew is part of a seperatists organization bent on destroying Corona. With some help from Rapunzel and Eugene, Cassandra manages to defeat Andrew and save the book. She is hailed as a hero for her efforts, receives a Medal of Honor, and becomes the talk of the kingdom, as a result.
By the time of "Secret of the Sun Drop", King Frederic has discovered that Cassandra was the one that leads Rapunzel over Corona's border wall and orders for her to be sent to a convent as punishment. Regretfully and with a heavy heart, the Captain abides by the king's decision, disappointing his daughter immensely. Before she can leave, however, the castle is attacked by a feral monstrosity sent by a now-villainous Varian. The Captain is injured during the attack, prompting Cassandra to take command of the guards in his place. Cassandra's bravery and competence earn her stay in the castle. Unfortunately, Queen Arianna had been kidnapped during the siege, prompting the King to issue an assault upon Varian. With the Captain wounded, Cassandra is chosen to assume his position and lead the assault, which she does confidently, with Eugene, Maximus, and Lance by her side.
Toward the end of the episode, Rapunzel defeats Varian and reconciles with her father. The rocks, meanwhile, form a path leading somewhere beyond Corona's walls, prompting Rapunzel to follow its trail.
Cassandra joins Rapunzel on her journey—as does Eugene, Lance, Hook Foot, and Shorty, much to Cassandra's chagrin. According to "Beyond the Corona Walls", Cassandra made a promise to King Frederic that she'll keep Rapunzel safe on their journey, and keeps to her promise with her usual protective and callous nature. She also eventually meets her match with Adira, an eccentric, yet skilled warrior that introduces herself as a guide for Rapunzel and her allies, whom Cassandra quickly starts to dislike.
In "Rapunzel and the Great Tree", Cassandra, Rapunzel and their friends stumble across the Great Tree. Upon getting inside of it, Adira reveals to the company that the tree once was a stronghold of the powerful dark sorcerer Zhan Tiri, thus making Cassandra even more suspicious about her. When she tries to tell Rapunzel to leave Adira, the princess refuses and tells Cassandra that she'll sometimes make decisions they won't always agree on, what makes the latter feel like she's waiting on the wings of Rapunzel and her friends.
When the sinister warrior Hector attacks the company, Cassandra fights back and ultimately pushes him off the ledge. However, Hector comes back, possessed by the Heart of Zhan Tiri's tree. Despite Cassandra's protests, Rapunzel decides to use the reverse incantation, that she found before the attack, to destroy the vines holding Hector. At that moment Cassandra notices a magic spear and tries to convince Rapunzel to let her use it against the tree, but the incantation's power proves itself to be way too uncontrollable for the princess to stop using it. In attempt to stop her, Cassandra touches Rapunzel's arm, but the incantation's destructive power severely burns her right arm, turning it pitch black. When everyone escaped from the falling tree, Cassandra finds a suit of armor and puts it on to protect her body from further pain. In the time following these events, Cassandra remains bitter, blaming Rapunzel for the events that transpired. Rapunzel tries to communicate with Cassandra about the tension between them, but the reserved Cassandra is hesitant to do so.
In "Mirror, Mirror", a powerful storm forces the group to take shelter in a peculiar inn hosted by a man named Matthews. During their time there, Cassandra comes across a room that sucks her inside. When she escapes, the house has been destroyed though Rapunzel and her friends are all safe. Rapunzel questions Cassandra on her absence, but she is quick to brush off any suspicion. Later, Rapunzel and Eugene are able to uncover the final piece of a scroll detailing Rapunzel's connection to the rocks with the help of Lord Demanitus. Before his departure, Demanitus warns Eugene that someone will betray Rapunzel before their journey comes to an end. Though Eugene has come to love Cassandra like an "annoying sister", he believes her to be the most likely candidate and warns Rapunzel about the matter in "Destinies Collide". Rapunzel believes Demanitus was wrong and continues forth to the Dark Kingdom, where she is destined to connect with the source of the black rocks (a life-killing opal) and restore balance to the world. Inside the Dark Kingdom's castle, Rapunzel, Eugene, and Cassandra approach the opal together. Before Rapunzel can touch it and fulfill her destiny, Cassandra grabs it, instead, declares that she's fulfilling her destiny and merges the opal with her body—magically altering her body, eyes and hair. Once the alteration is over, Cassandra sinisterly tells Rapunzel that she should have been careful who she trusted.
- Interestingly, Cassandra's will to protect Rapunzel at all costs is also quite damaging, specifically with the relationship Rapunzel shares with Eugene. Because of Cassandra's distrust toward Eugene, the former actively advises Rapunzel to keep secrets from him, which in turn cripples the amount of trust shared between the two; though Cassandra blames Eugene for failing to address Rapunzel's personal struggles, it is impossible for him to do so if Rapunzel refuses to be honest with him. Though Rapunzel is at fault for choosing to keep secrets, Cassandra is also at fault for encouraging the princess' will to do so. This was addressed in "What the Hair?!".
- The name Cassandra means "praise of men" in Greek.
- In "Rapunzel's Enemy" and "Fitzherbert P.I.", it is shown that Cassandra respects Corona's history a great deal, and considers it an esteemed honor to uphold the kingdom's traditions.
- According to "Great Expotations", Cassandra has been training to join the guard since she was six.
- In "Keeper of the Spire", she is revealed to be four years older than Rapunzel.
- Cassandra is the second of Rapunzel's allies to turn against her, the first being Varian.