Kleissu was a male Mizarian scientist, noted for his efforts to formulate a unified theory of the nature of the universe.
In the late 2370s, his theories were discovered by B'Ekara, a Klingon scientist at the Klingon Science Institute. However, because of the Klingon Empire's policies toward the pacifistic Mizarians, B'Ekara was fired for referencing his work, and the continuation of her research banned. Both Kleissu and B'Ekara later joined the Matter of Everything (or HapHoch) to continue their work. (ST novel: Articles of the Federation)