Nessus is a male character in Larry Niven

Larry Niven

Laurence van Cott Niven / ˈlæri ˈnɪvən/ is an American science fiction author. His best-known work is Ringworld , which received Hugo, Locus, Ditmar, and Nebula awards. His work is primarily hard science fiction, using big science concepts and theoretical physics...

's Known Space

Known Space

Known Space is the fictional setting of some dozen science fiction novels and several collections of short stories written by author Larry Niven. It has also in part been used as a shared universe in the Man-Kzin Wars spin-off anthologies sub-series....

 universe, of the species Pierson's Puppeteer

Pierson's Puppeteer

Pierson's Puppeteers, often known just as Puppeteers, are a fictional alien race from American author Larry Niven's Known Space books.- Biology and sociology :...

, an herbivorous

Herbivore

Herbivores are organisms that are anatomically and physiologically adapted to eat plant-based foods. Herbivory is a form of consumption in which an organism principally eats autotrophs such as plants, algae and photosynthesizing bacteria. More generally, organisms that feed on autotrophs in...

 species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 noted for two heads whose mouths act as capable hands. Pierson's Puppeteers are technically advanced in most of the physical sciences.

Nessus, like all Puppeteers ever met by humans, is insane by Puppeteer standards. Those who are sane are far too sensible (read "cowardly") to go off-world or interact with non-Puppeteers. Nessus demonstrates traits that in humans would be diagnosed as schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

, manic-depressive disorder

Bipolar disorder

Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...

, displacement

Displacement (psychology)

In Freudian psychology, displacement is an unconscious defense mechanism whereby the mind redirects effects from an object felt to be dangerous or unacceptable to an object felt to be safe or acceptable...

, and at times, extreme suggestibility

Suggestibility

Suggestibility is the quality of being inclined to accept and act on the suggestions of others.A person experiencing intense emotions tends to be more receptive to ideas and therefore more suggestible. Generally, suggestibility decreases as age increases...

.

Nessus is featured in the short story "The Soft Weapon

The Soft Weapon

"The Soft Weapon" is a science fiction short story written in 1967 by Larry Niven, set in his Known Space universe. It was the basis of the Star Trek: The Animated Series episode, "The Slaver Weapon"...

" (printed in the 1968 collection Neutron Star) and is also one of the expeditionaries to the Ringworld

Ringworld

Ringworld is a Hugo, Nebula, and Locus award-winning 1970 science fiction novel by Larry Niven, set in his Known Space universe and considered a classic of science fiction literature. It is followed by three sequels, and preceded by four prequels, and ties into numerous other books set in Known Space...

 in the 1970 book of the same name. Nessus is a central character in the novels Fleet of Worlds

Fleet of Worlds

Fleet of Worlds are both a location and a book in Larry Niven's Known Space series.The series consisting of this book and its sequels is referred to by the same title.-Novel:The novel, co-written by Niven and Edward M. Lerner, was released in 2007...

and Juggler of Worlds

Juggler of Worlds

Juggler of Worlds is the sequel novel to Fleet of Worlds by Larry Niven and Edward M. Lerner.It is set in the Known Space universe. Most of the book revisits earlier stories...

, as well as a tangential character in Destroyer of Worlds

Destroyer of Worlds (novel)

Destroyer of Worlds is a novel set in the Known Space series, by Larry Niven and Edward M. Lerner. It is a sequel to their previous novels, Fleet of Worlds and Juggler of Worlds...

and Betrayer of Worlds

Betrayer of Worlds

Betrayer of Worlds is a novel set in the Known Space series, by Larry Niven and Edward M. Lerner. It is a sequel to their previous novels, Fleet of Worlds, Juggler of Worlds, and Destroyer of Worlds., and is set 70 years before Ringworld....

, set almost 200 years before Ringworld

Ringworld

Ringworld is a Hugo, Nebula, and Locus award-winning 1970 science fiction novel by Larry Niven, set in his Known Space universe and considered a classic of science fiction literature. It is followed by three sequels, and preceded by four prequels, and ties into numerous other books set in Known Space...

.