Zack Addy is introduced as Dr. Brennan's graduate student and assistant at the Jeffersonian Institute at the start of the series. In the second season, he receives his doctorate in Forensic Anthropology and mechanical engineering and becomes a professional forensic anthropologist. Zack is closer to the stereotypical geek than anyone else on the team. Although well-meaning, helpful and friendly, when a situation calls for social interaction or intuition, he is often lost. During the course of events leading up to the death of Howard Epps, Zack was almost killed when he unwittingly triggered a pressure sensor tied to a bomb affixed to the headless body of Caroline Epps, only to be saved by Booth.

He is extremely intelligent; in episode 11 it is said that his IQ is significantly above 163 (which is already a genius level). He is also Hodgins' best friend, and lives in the upper part of Hodgins' garage. Zack was removed from his position on Dr. Brennan's team during the Gormagon episodes. Zack is also known as "Zacharoni", "Z-Man", and competes with Hodgins for "King of the Lab".