Lucifer is a demon and the eldest of the seven demon brothers in the world of Obey Me!. He holds the title of first-born and is the most powerful among his siblings. He is also known as the Avatar of Pride, the embodiment of that sin, and serves as the vice president of the student council at the Royal Academy of Diavolo, commonly referred to as RAD. Lucifer is the closest friend and right-hand man of Diavolo, the prince of the Devildom, and he is fiercely loyal to him. His physical appearance includes black hair with white-tinted tips parted on the right side, and black eyes with an outward red gradient. He is the second tallest of the brothers, nearly reaching Beelzebub in height, and he paints his nails red, a habit shared by all the brothers.

Lucifer's personality is defined by his immense pride, which manifests as confidence, assertiveness, and a commanding presence. He is responsible, calm, and strict with his brothers, often acting as a disciplinarian to keep them in line, sometimes using force when necessary. Despite his harsh exterior, he is deeply protective of his family and cares for them, though he often expresses this through sternness rather than warmth. He is described as a sadist with a malicious streak, but also as someone who tolerates his brothers' rule-breaking if done with good intentions, occasionally pretending not to notice or even helping them. His pride can lead to vulnerability, and he struggles to show his softer side.

His primary motivations are his loyalty to Diavolo and his sense of duty as the eldest brother. He strives to protect those he cares about, especially his family, and works to maintain order within the Devildom. As a figure of authority, he takes his responsibilities seriously, even when he personally dislikes certain tasks, and he fulfills his role as the student council vice president with diligence. His deep desire for ownership and control is another facet of his personality, stemming from his pride.

In the story, Lucifer plays a central role as the leader of the demon brothers and as Diavolo's trusted ally. He is a key figure in the main narrative, often overseeing the exchange program that brings humans and angels to RAD. His position as the eldest brother means that the family's reputation rests on his shoulders, and he works to keep the brothers united, even if it requires force.

Key relationships include his bond with Diavolo, which is marked by mutual respect and centuries of friendship, though Lucifer often complains about Diavolo's requests. His relationship with his brothers is complex: he is stern and authoritarian with them, particularly with Mammon, whom he frequently reprimands, yet he harbors deep affection for all of them. He has a notable rivalry with Satan, who resents him, and he imprisoned Belphegor in the attic after a past conflict. His interactions with the main character show his growth, as he gradually opens up and learns to trust, revealing a more tender and teasing side.

Throughout the series, Lucifer undergoes development as he confronts his pride and vulnerability. Key story arcs, such as the Celestial War, highlight his commitment to family and his willingness to make difficult choices. He learns to balance his pride with responsibility and becomes more emotionally accessible, though he never fully sheds his dignified, prideful nature.

Lucifer possesses formidable abilities, including exceptional combat skills and the power to manipulate both light and darkness. He is a highly strategic and adaptable fighter, and his powers evolve as the story progresses. However, his pride can also be a limitation, leading to conflicts with allies and enemies alike.