Doug Hummer is a notable member of the secret organization Libra, a group dedicated to maintaining order in the chaotic city of Hellsalem's Lot. His existence is highly unusual, as he shares a single body with a notorious serial killer named Deldro Brody. This bizarre condition is the result of an experiment by a powerful entity known as the "Paranoid Queen" Aligura, who sought to create the perfect partner. She liquefied the "bad boy" personality of Deldro Brody and implanted him into the handsome and physically ideal Doug, believing the combination of great looks and a wild personality would be ideal. However, the experiment did not go as planned, as the two individuals who emerged from it had no interest in their creator and instead escaped together, forming their own powerful partnership.

In terms of appearance, Doug is a slim young man with short, grey hair, silver eyes, and light brown or dark skin. His typical attire consists of a long-sleeved white shirt with the sleeves rolled up to his elbows, paired with blue skinny jeans. Despite his imprisonment, Doug is known for having a surprisingly cheerful, polite, and open personality. He is often described as lively and communicates with a refreshing directness, commonly using a single, simple phrase to express his feelings. His good nature is particularly remarkable given that he is an innocent man forced to live in a high-security prison because of the dangerous entity within him, a situation he accepts without complaint. His physical attractiveness is so significant that it has earned him the nickname "Perfect Man," and he effortlessly charms many female characters, including his fellow Libra members K·K and Chain Sumeragi, as well as his own female prison warden, who is known to blush in his presence.

The core of his role in the story is as a member of Libra, though he and Deldro are typically kept sealed in the deepest part of Hellsalem's Lot's largest prison due to the threat Deldro represents. They are only called upon to assist the organization in the most dire and desperate situations, acting as a secret weapon of immense power. His most significant relationship is, by necessity, the one he has with Deldro Brody. Despite the circumstances of their forced union, they have developed a relationship of profound trust and mutual reliance, describing themselves as being "of one heart and one body". Deldro can partially manifest from Doug's body, most notably appearing from slits on Doug's wrists to converse with the outside world or to combine with him for combat.

Doug's development is less about a linear emotional arc and more about the stable, functional partnership he maintains with the killer inside him, which directly contrasts with the intentions of their creator. His primary motivation is simply living his life alongside his "good buddy". His notable ability, used in tandem with Deldro, is called Exocrimson, also known as the "Blood Hammer". This power allows Doug to use the special blood that is Deldro's liquefied body to form a gigantic, powerful exoskeleton armor around himself. This armor grants him immense superhuman strength and durability. A basic but devastating technique using this form is called the "Plain Punch - Revised," where Deldro shapes his hand into a giant, hardened crimson fist to strike his opponents. Together, Doug and Deldro are an inseparable pair, a living weapon of immense power who prefer a quiet life of confinement to the chaos they were literally built to embody.