Gluttony is a homunculus, an artificial being created by the entity known as Father. He embodies the sin of gluttony, and his very existence is defined by an endless, ravenous hunger. Unlike some of his siblings who were crafted with specific purposes, Gluttony was originally a failed experiment by Father, who attempted to create his own replica of the Gate of Truth, the source of all alchemical knowledge and power. This failure resulted in Gluttony's unique and aberrant abilities. His physical appearance reflects his nature, being short, obese, and bald with white, pupil-less eyes and oversized teeth. The symbol of the Ouroboros, representing his status as a homunculus, is tattooed on his tongue.

Gluttony’s personality is strikingly child-like and simple-minded. He is dim-witted, naive, and generally meek, content to follow orders from his fellow homunculi without question, especially those from Lust, to whom he is deeply attached. His primary motivation and only true interest lies in eating. He sees the world in two simple categories: things he is allowed to eat, and things he is not. Living creatures, particularly humans, are his preferred food, with a noted fondness for women, whom he claims taste softer. While he can appear almost innocent and even friendly when not eating, this is a fragile state. Any resistance to his hunger or a direct order can trigger vicious, mean-spirited aggression, and against someone he truly hates, he can fly into a terrifying, berserker rage.

Within the narrative, Gluttony serves as a loyal and effective agent of Father. His enhanced sense of smell makes him an invaluable tracker, capable of locating specific individuals over great distances or in complete darkness. He is also often tasked with disposing of evidence, using his powerful jaws to devour anything from steel and buildings to the diamond-hard carbon of Greed’s shield. His role frequently places him on the front lines, where he acts as a powerful if unintelligent enforcer, often alongside Lust and later Envy. He is a persistent threat to the protagonists, hunting Scar, battling the Elric brothers and their allies, and showcasing his terrifying power in several key encounters.

Gluttony's most significant relationship is with Lust. He is rarely seen far from her, looking up to her as an older sister or even a mother figure, and he is utterly devastated by her death. He shows a genuine, if simple, fondness for all his homunculus siblings, though this affection is not always returned. His interactions with others are purely transactional, based on whether they are a potential meal or a person he is forbidden to eat. His hatred for Roy Mustang, who killed Lust, is one of the few complex emotional drives he displays, pushing him into a frenzy of revenge.

The most significant development in Gluttony’s story is the revelation of his true nature. When sufficiently angered or threatened, he opens his incomplete Gate of Truth. A massive maw splits open his torso from his lower jaw down his belly, revealing monstrous fang-like ribs and a giant eye. This eye fires a powerful vortex that sucks everything in its range into a seemingly endless, dark, and wet dimensional void inside his body—an imperfect replica of the real Gate of Truth. This ability is his ultimate weapon, which he uses to accidentally swallow Edward Elric, Ling Yao, and Envy, forcing Alphonse Elric to reluctantly lead him to Father in a desperate attempt to retrieve them. Despite his immense power, Gluttony is ultimately defeated not by a hero, but by his own brother. Late in the conflict, Pride, finding Gluttony’s Philosopher Stone nearly depleted after numerous regenerations, coldly and remorselessly devours him to absorb his lingering power and enhanced sense of smell. In his final moments, Gluttony reverts to a frightened child, begging for his life and calling out for Lust.

Gluttony possesses the standard homunculus abilities, including a Philosopher's Stone core that grants incredible regenerative capabilities, allowing him to heal from almost any wound as long as the stone has power. Despite his obese frame, he is remarkably strong, fast, and agile, able to crush opponents with body slams and punch with tremendous force. His most notable abilities, beyond his regeneration, are his superhuman sense of smell, his powerful jaws that can consume virtually any material, and his ultimate technique: the opening of his false Gate of Truth to create a massive, all-consuming vortex.