Gluttony is a homunculus, an artificial being created from a Philosopher's Stone, who embodies the concept of insatiable hunger. He is a failed experiment by his creator, known as Father, who intended to replicate the Gate of Truth, the ultimate source of alchemical knowledge. This failure resulted in Gluttony's unique and devastating abilities, but also in a childlike and simplistic mind.

Physically, Gluttony is short, obese, and bald, with vacant white eyes, oversized teeth, and the symbol of the Ouroboros marked on his tongue. Despite his heavy and often clumsy appearance, he possesses considerable strength, speed, and agility. His immense physical power allows him to crush opponents with body slams and throw heavy objects with ease, while his powerful jaws can chew through almost any material, including wood, steel, and even the diamond-hard carbon skin of his fellow homunculus, Greed.

His personality is defined by a ravenous, never-ending hunger and a dim-witted, childlike demeanor. He is generally meek and obedient, content to follow the orders of his superiors and find something to eat in the process. He does not seem to fully grasp the moral weight of his actions, innocently dividing the world into two categories: those he is forbidden to eat and those who are potential meals. While he can be friendly when not hunting, his interest in anyone he is not allowed to consume is minimal. However, this childlike nature can give way to viciousness when he is hungry or angered, and he displays mean-spirited enjoyment when attacking his prey. When faced with someone he truly hates, such as Roy Mustang for killing Lust, he flies into a terrifying, berserker rage.

His primary motivation is simply to eat, especially living creatures, and he has a particular fondness for the taste of women. He serves the homunculi as a field agent, using his exceptional sense of smell to track targets from great distances and his powerful jaws to devour evidence, such as the ruins of an entire kingdom. His most notable ability, however, is his incomplete "false Gate of Truth." When enraged or pushed, a massive hole opens from his lower jaw down to his abdomen, revealing a giant eye and rib-like fangs. This gate creates a powerful vortex that sucks anything in its range into an endless, dark, dimension-like void within his body, a failed replica of the true Gate of Truth.

Within the homunculus family, Gluttony shares a deep and genuine bond with his siblings, though this affection is not always returned. He is almost never seen apart from Lust, whom he looks up to like an older sister or mother figure, and he becomes distraught and grief-stricken after her death. He works alongside others like Envy and later Pride, responding to their commands. His simple-minded loyalty ultimately leads to his demise; when he is severely weakened in a battle, Pride consumes him without remorse to absorb the remaining power of his Philosopher's Stone and gain his acute sense of smell. His final, desperate words are a cry for Lust to save him.