Cassius Warrington was a wizard and a student in Slytherin House at Hogwarts School of Witchcraft and Wizardry. He was known for his large, brutish physique and his antagonistic relationship with Harry Potter and his allies. Warrington's most notable actions include attempting to become the Hogwarts champion in the Triwizard Tournament and later serving as a member of Dolores Umbridge's oppressive Inquisitorial Squad.
Cassius Warrington was a student at Hogwarts at least two years ahead of Harry Potter. During the 1994-1995 school year, the Triwizard Tournament was held at Hogwarts. As the competition was only open to students aged seventeen and over, Warrington was among the older students who placed his name into the Goblet of Fire in an attempt to be selected as the Hogwarts Champion. He was ultimately not chosen. In the 1995-1996 school year, Warrington joined the Inquisitorial Squad, a group of students, primarily from Slytherin, who were handpicked by High Inquisitor Dolores Umbridge to enforce her draconian regulations. As a member, he held the power to dock points from other students, including prefects. He actively participated in the squad's efforts to undermine Dumbledore's Army. When the Inquisitorial Squad discovered the location of the D.A.'s secret meetings in the Room of Requirement, Warrington was part of the group that ambushed and captured its members. Later that year, after Fred and George Weasley set off a portable swamp and a cascade of magical fireworks in the castle as a final act of rebellion, Warrington and Crabbe were responsible for physically seizing the twins. During the ensuing chaos as the Weasleys made their dramatic escape on their broomsticks, a furious Umbridge attempted to hit them with an Impediment Jinx but missed, striking Warrington in the face instead.
Warrington is described as a “great hefty bloke.” George Weasley memorably commented that he “looks like a sloth.” His personality reflects that of a typical Slytherin bully. He was confrontational, aligned himself with authority figures like Dolores Umbridge for personal power, and clearly enjoyed the opportunity to intimidate and punish students from other houses, particularly Gryffindor. His willingness to join the Inquisitorial Squad demonstrated his support for Umbridge's oppressive regime and the Ministry of Magic's campaign against Albus Dumbledore and Harry Potter.
Warrington's precise level of magical skill is not detailed, but certain inferences can be made.
Warrington was a loyal member of Slytherin House and was part of the circle of students that included Draco Malfoy, Vincent Crabbe, Gregory Goyle, and Pansy Parkinson. He was a staunch ally of Dolores Umbridge during her tenure at Hogwarts. Conversely, he was an enemy to Harry Potter, the Weasley family, and all members of Dumbledore's Army. He was directly involved in the physical capture of Fred Weasley and George Weasley.