Tereus is a prototype military bioroid of a new generation, created primarily using genetic material from the cyborg soldier Briareos Hecatonchires. His physical form is identical to Briareos' original human appearance prior to cybernetic enhancement.

Developed to combine peak human physical and mental capabilities while eliminating negative emotional traits detrimental to combat effectiveness, Tereus was built on the assessment that Briareos possessed optimal qualities for E-SWAT operations. Consequently, he exhibits personality traits, behavioral patterns, mannerisms, and emotional responses closely mirroring Briareos. This resemblance causes significant confusion and discomfort for Deunan Knute when they are assigned as partners.

Initially deployed as a temporary replacement for Briareos during medical recovery, Tereus undergoes field evaluation partnered with Deunan. His operational duties involve Olympus counter-terrorism, specifically investigating attacks linked to mind-control signals transmitted via the consumer device Connexus. He consistently demonstrates superior physical capabilities per his design and a characteristically calm, duty-focused bioroid demeanor.

Interpersonal tensions arise as Tereus develops feelings for Deunan that mirror Briareos' emotions, creating a complex dynamic. Direct confrontation is avoided due to mutual acknowledgment of operational necessity. Over time, Tereus gradually establishes a distinct identity beyond being a genetic replica, evolving into an autonomous individual. His actions assisting Deunan and Briareos during the Halcon crisis against the mind-control threat further cement his status as a separate entity with independent agency.

The narrative's resolution confirms his transition into a unique individual, recognized by both Deunan and Briareos as having moved beyond his original designation as a prototype.