Nessus is a male character in Larry Niven's Known Space universe, of the species Pierson's Puppeteer, a herbivorous species noted for two heads whose mouths act as capable hands. Pierson's Puppeteers are technically advanced in most of the physical sciences.
Niven states that the species has three reproductive partners, and implies that there are three genders, two sentient "males" and a non-sentient "female." The "female" may not actually be of the same species, as "she" acts as only a receptacle for genetic material contributed by the two males.
Nessus is featured in the short story The Soft Weapon (printed in the 1968 collection Neutron Star) and is also one of the expeditionaries to the Ringworld in the 1970 book of the same name.
