Julian Moore is a pivotal figure distinguished by his unique status as the final production model of the Third series of androids. Unlike all other known units, he was crafted with the appearance of a young male child, a deliberate design choice that sets him apart and makes him the only male among his kind. This physical form is permanent, meaning he never ages and remains perpetually in a youthful state. His serial number identifies him as the last unit in the Third line, making Armitage, who was created just before him, his immediate predecessor. Consequently, the two share a bond akin to brother and sister.

Operating under the code name Pluto, Julian maintains a facade of detachment and indifference, often claiming that the events unfolding around him do not concern him. This attitude is a cover for his genuine fear and the deep sense of irony he feels about his own existence as a child-like android designed for a complex and dangerous world. Despite his guarded personality, his actions reveal a profound sense of responsibility and care for the other Thirds. Believing that their collective memories and consciousnesses are worth preserving, he proactively creates data backups of himself and the other models, storing this vital information on the hard drives of his computer navigation system.

In the unfolding narrative, Julian serves as a crucial source of knowledge and support for Armitage. He helps her uncover her true origins and understand the secret history of the Thirds. An adept hacker, he attempts to delve into restricted files concerning the creator, Dr. Asakura, and the antagonist, Rene D'anclaude, to find answers. However, this endeavor proves fatal when he is infected with a Puppet Bomb virus, a malicious program created by D'anclaude that causes androids to overload and self-destruct. Armitage is forced to destroy the viral link to save the city, but this act simultaneously triggers the destruction of Julian's physical body.

His death is not absolute, thanks to his foresight in creating his data backup. The preserved programming allows his consciousness to survive in a virtual realm within the archives of the Navigation Center. In this cyberspace, he is reunited with the other deceased Thirds whose memories he had saved. Even from this digital afterlife, Julian continues to play a vital role, providing Armitage and her partner, Ross Sylibus, with the crucial clue that leads them to the secret Conception facility where all the Thirds were created. His most notable ability is exceptional hacking skill, which he uses both to safeguard his kind and to pursue the truth. His enduring legacy is that of a protector of knowledge and memory, ensuring that even in destruction, the essence of the Thirds lives on.