Cleo de Nile is the main antagonist of Volume 1 of the Monster High webseries as well as the first TV special "New Ghoul @ School".
The daughter of the mummies, Cleo de Nile is the queen bee of Monster High. When Frankie first comes to Monster High, Cleo immediately took a disliking to her and especially when Frankie flirted with Deuce, not knowing he and Cleo were together. Cleo continued her hatred for Frankie and was the main antagonist of the series up until the second volume of the series when she became friend and Toralei Stripe took on the role. Cleo is now the series anti-hero and occasional antagonist, though she is no longer a villain.