TV-Series
Description
Professeur Thésalonixus, known as Professor Cobra in the Japanese version and Professor Thelonious Viper in the English version, is a dueling instructor who serves as the main antagonist of the opening arc of the third season of the anime Yu-Gi-Oh! GX. He arrives at Duel Academy at the invitation of Chancellor Shepard, presented as a demanding teacher from the rival West Academy whose harsh methods are intended to push students toward their full potential.

Thésalonixus is a former special forces soldier and an ex-military commander. During a mission, his comrades discovered an abandoned baby and went in another direction, where they were killed by a bomb. Thésalonixus took the child in and adopted him, naming him Pierce. Pierce became the center of his life, but the boy later died, leaving Thésalonixus overwhelmed by grief. Desperate to bring his son back, he formed a pact with the malevolent spirit Yubel, who promised to help him resurrect Pierce in exchange for his cooperation.

He is a man of strong build with a menacing and intimidating presence. He projects the image of a ruthless, no-nonsense authority figure who believes that hard work, discipline, and intense training can accomplish anything. Beneath this harsh exterior lies a grieving father, and his personal loss is the driving force behind his otherwise cruel behavior. This grief explains the desperation behind his actions, even as he endangers others in pursuit of his goal.

His role in the story begins as that of a feared new teacher, but it gradually becomes clear that he is the architect of a sinister scheme. Under the guise of training, he forces students to wear Bio-Bands, devices that drain their life energy whenever they duel. That stolen energy is channeled to Yubel, who uses it in the effort to restore Pierce. His plan places the entire student body in danger, and he clashes with the main characters as they work to uncover the truth. The plot is ultimately stopped when Thésalonixus is defeated in a duel by Jaden Yuki, the protagonist.

His key relationships revolve around Pierce, whose memory motivates his entire crusade, and Yubel, the supernatural ally who exploits his grief. He interacts with the students of Duel Academy primarily as a stern teacher and later as a threat to their lives, while his relationship with Chancellor Shepard is built on the pretense that his purpose is to improve the school.

As a duelist, Thésalonixus is highly skilled and ruthless, using a snake-themed deck built around venom counters. His signature cards include Vennominon the King of Poisonous Snakes and the Snake Deity's Command, which allow him to weaken opponents over time. His military background gives him a disciplined and tactical approach to dueling, and his Bio-Bands represent an additional, non-card-based method of harming opponents by draining their energy.