Koro-sensei is the enigmatic protagonist of 'Ansatsu Kyoushitsu' (Assassination Classroom). He is a yellow, octopus-like creature with superhuman speed and strength who becomes the homeroom teacher of Class 3-E at Kunugigaoka Junior High School. Despite his threat to destroy the Earth within a year, Koro-sensei is a compassionate and wise mentor, dedicated to helping his students grow academically and personally. His cheerful personality, unique teaching methods, and mysterious past make him a beloved and memorable character in the series.