His dark path is rooted in wartime tragedy in Lithuania, specifically the brutal murder and cannibalism of his younger sister Misha by deserters. Exhibiting traits of Antisocial Personality Disorder (ASPD) and extreme narcissism, he maintains absolute emotional control and an orderly routine. He divides people into intellectual beings and the "rude" or dull, whom he views as livestock fit for consumption.

Reconstructs crime scenes by stepping directly into the minds and motives of killers. Prefers the company of stray dogs over humans and struggles with standard interpersonal connections. Wrestles with the secret pleasure he feels after killing, fearing he understands monsters because he shares their nature.

Head of the FBI's Behavioral Science Unit, Crawford views people as instruments necessary to catch monsters. Jack repeatedly sacrifices Will Graham's psychological well-being, pushing him into dangerous empathy loops despite knowing the severe toll it takes. Entrusted Dr. Hannibal Lecter to protect and monitor Will, completely missing that Lecter was the ultimate monster (the Chesapeake Ripper) right under his nose.

Acts as Will Graham’s friend and colleague, fiercely protective of his mental health while blindly trusting her former mentor, Hannibal Lecter.

Partnered often with Jimmy Price, Zeller uses his medical background to autopsy gruesome remains, bringing a grounded, blue-collar realism to the Behavioral Analysis Unit (BAU). He frequently breaks high-tension dramatic moments with cynical banter, casual wisecracks, and lighthearted sarcasm. Zeller resents Will’s unique intuitive profiling gifts and the preferential treatment/attention Jack Crawford shows him, which pushes Zeller to leak details to tabloid journalist Freddie Lounds. He relies strictly on empirical evidence, creating a thematic contrast against Will’s terrifyingly empathetic, psychological approach to reconstructing murders.

Worked for the Behavioral Analysis Unit (BAU), using meticulous lab work, fiber traces, and autopsies to decode crime scenes. Relied strictly on hard evidence and facts, contrasting with the empathetic or psychological profiling used by Will Graham and Alana Bloom. Proved highly capable outside the lab, showing strong firearm proficiency and quiet courage. Formed a unique working bond with Will, often checking up on his well-being and serving as the sole team member he called when doubting his own sanity.