While her sister Katarina has always been the most celebrated member of the household, the Du Couteau family has a long history of service to Noxus. It has often been said that no soldier has ever been as fortunate as General Du Couteau to have been graced with daughters. His youngest, Cassiopeia - despite lacking her sister's killer instincts - was equally renowned in at court for her stately character and elegance. Cunning as she was beautiful, the temptress could never be found far from the arm of any foreign dignitary, her wiles prying secrets from the lips of even the most wary attaché. With the Noxian barbarian pacification campaign having ground to a standstill, Cassiopeia had set her sights on a diplomat from a tribe of the Freljord region. Thinking him an easy mark, the scheming seductress set about beguiling him. He refused to confide in her, however, until she swore an oath of secrecy upon his sword - a strange weapon with a serpentine curve to the blade.
Once her tryst was over, Cassiopeia provisioned her father with information regarding the barbarian resistance. As she divulged this intelligence, a wave of revulsion washed over her. She screamed in agony as her silky skin hardened to scales, her lustrous hair thickened to leather, and her manicured fingernails sharpened to claws. Dazed, she fell upon a group of horrified servants, rending them limb from limb in a heartbeat. When it was over the blood soaked figure was no longer the ravishing jewel of the Noxian court, but a horror trapped somewhere between woman and serpent. Unable to serve in her traditional capacity, Cassiopeia departed for the League, continuing her service to Noxus on the Field of Justice.
"Though she may have appeared the innocent flower, she was the serpent under it." - Katarina, the Sinister Blade