A high school teacher who constantly thinks of self-destruction while he continues teaching his class about despairing things with an overreacting response.
He is the youngest son and second youngest of the Itoshikis, a distinguished family in Kuraizawa, Shinshū Prefecture, with two older brothers, and a younger sister. He teaches a class full of eccentric, idiosyncratic students who put him through a lot of trouble. Instead of actually teaching his class, he tends to go off topic into lecturing about a problem in society.
Nozomu constantly attempts suicide because he is extremely pessimistic and paranoid. Despite his negative view on things, he does not seriously try to kill himself since he is often stopped by one of his students. He continually scolds and rants about different aspects of life and Japanese culture and will often say that he is "in despair! "
Itoshiki was created by the mangaka Koji Kumeta for use in the series Sayonara, Zetsubou Sensei, and is the titular "Zetsubou Sensei", or Despair Teacher. Vertically, the characters in his name are inauspicious, predicting bad luck for him. Horizontally, however, the characters in his name spell zetsubou, or despair. Itoshiki was based off of the main character from Dazai Osamu's No Longer Human, which is the favorite novel of both the character and the mangaka himself. In the anime, Itoshiki is voiced by Hiroshi Kamiya.