Hexadecimal, the self-proclaimed "Queen of Chaos", is a virus operating out of Lost Angles. She is Megabyte's sister, serving as the chaos to his order. Her origin is revealed in the fourth season.
She is voiced by Shirley Millner.
She and Megabyte were once one virus (Kilobyte), who was scheduled for deletion by the Guardians, but upgraded to Gigabyte before it could be carried out. He mortally wounded Bob's partner and moved in toward Bob before being accidentally teleported away by Welman Matrix's gateway device. The results were devastating: the destruction of Mainframe's twin city (creating Lost Angles), everyone present being nullified (including Welman, who became Nibbles), and Gigabyte being split into Megabyte and Hexadecimal. Upon being separated, Hexadecimal observed her surroundings and (with a mask change) exclaimed, "I like it here!".
Hexadecimal is melodramatic and extremely emotional, able to switch emotions by a simple wave of her hand (which changes the mask she wears, and her emotions along with it). The masks change constantly in a slew of different ways, usually while obscured from the home viewer. Episodes 1 and 10 of season 2, and episode 4 of season 3 showed her mask changing on screen in an instant. She has transfinite power reserves, meaning that she has near limitless stores of energy to draw from, and as such, is quite powerful herself. Her powers include energy beams and fireballs, altering gravity (once causing Bob to stop and hover in midair) and being able to fly, shrugging off severe damage and controlling nulls (sprites downgraded to slug-like status for losing to the User in a game). She also has the power to open a portal to the net or web in her "looking glass", and has also been seen taking control of system programs like the system paint program. It is suggested that her powers are near infinite, but because of her madness she is unable to use them for anything constructive.
Her vast collection of masks serve to show her facial expression, thereby giving her a harlequin-like appearance. The expressions shown in these masks can range from happy, sad, scheming, and even homicidal rage. These masks also hold her power in check. When removed (as in the episode "Painted Windows"), her power escapes and continues to do damage to her environment, and she will overload and be destroyed if the mask is not replaced.
She is a benign virus, meaning she does not infect other entities. Instead, her primary motive is to simply cause random chaos for fun (and also to kill Megabyte, who kept trying to kill her, likely due to simple sibling rivalry). Due to her power and insanity, her fun nearly always led to Mainframe crashing. She even once nearly caused it unwittingly, when a Web Creature emerged from her mirror and possessed her. All of the nulls sensed this danger and covered her completely. The giant "Nullzilla" monster went on a rampage, as (according to Dot) the possessed-Hexadecimal was trying to escape.
Eventually Bob the Guardian defragmented her coding, which "healed" her insanity, merging all her "expression masks" into a normal face as well as altering her outfit from mostly red to white. She was issued a System Icon, which effectively made her a system-protected "citizen of Mainframe". Out of gratitude she not only developed an intense romantic interest in Bob, but to undo the larger danger of the super-virus Damien, she spread herself onto the net to undo Damien's internet damage. Ultimately successful, she is presumed decompiled and deceased. Certainly she faced the risks of her decision as a suicidal sacrifice for the greater good, her last action that of a hero.