Greed is one of the seven homunculi, artificial beings created through alchemy, and embodies the sin of avarice. His name is a direct representation of his core driving force: an unquenchable desire to possess everything the world has to offer, including material wealth, power, status, women, and ultimately, immortality. He is distinguished from his fellow homunculi by his fierce independence. Dissatisfied with serving under his creator, Father, Greed rebelled and left their hidden lair nearly a century before the events of the story, choosing to carve his own path in the human world.

In his original form, Greed’s appearance is that of a tall, well-built man with spiky hair, often seen wearing sunglasses and a fur-lined coat. The Ouroboros tattoo, the mark of a homunculus, is located on the back of his left hand. His personality is complex, balancing his self-serving nature with a unique set of principles. He is known for being laid-back, casual, and even charming when he chooses to be, but he can quickly shift to being menacing and violent when his desires are threatened. He maintains a personal code against lying and typically avoids fighting women, a rule that stems from his own standards rather than altruism. Despite being a villain, he is neither cruel nor sadistic without cause. He operates with a degree of honesty and straightforwardness that makes him one of the more approachable and understandable antagonists in the series.

A critical aspect of Greed's character is his relationship with his subordinates. Unlike other homunculi who view humans as tools or insects, Greed, in his own possessive way, values the band of outcasts and chimeras who work for him. He refers to them as his "possessions," which, in his mind, is the highest form of appreciation. He offers them protection and a sense of belonging when they have nowhere else to go, and in return, they are fiercely loyal to him, viewing him as a friend rather than a master. This bond highlights a nuanced facet of his greed: it is not just for money or objects, but for meaningful connections and loyal companionship.

Greed's primary motivation is to obtain "everything," but his story arc forces him to confront what that truly means. Initially, his goal is wrapped up in worldly pleasures and eternal life. His role in the story begins as a minor antagonist; he establishes a base of operations called the Devil's Nest in the city of Dublith. He captures Alphonse Elric to learn the secrets of immortality, which leads to a conflict with Edward Elric. However, this independence is short-lived. The homunculus known as Wrath, who is also the Führer of the nation, storms the Devil's Nest. Wrath’s "Ultimate Eye" allows him to see and exploit the brief openings in Greed's defense, and Greed is ultimately defeated, captured, and forcibly returned to Father. Father then destroys Greed’s physical body but holds onto his core consciousness—the Philosopher's Stone that defines his existence—for future use.

The most significant development for Greed occurs when Father offers him a new body. This new vessel is the dying prince Ling Yao, a young man from the nation of Xing who came to Amestris in search of immortality. Greed is implanted into Ling's body, and the two beings share one form. Initially, Greed's memories are suppressed, and he serves Father once more. However, after encountering a former subordinate from his past life, his memories resurface, and his rebellious nature reignites. This leads to a unique partnership where Greed and Ling must learn to coexist and cooperate, creating a combined personality often nicknamed "Greedling" by fans. For the latter half of the story, this fused being becomes a crucial ally to Edward and Alphonse Elric.

Through this alliance and his shared existence with Ling Yao, Greed undergoes his greatest development. He begins to realize that his true desire was never for godlike power or material riches, but simply for irreplaceable friends and a sense of belonging. In his final battle against his creator, Father, Greed experiences a moment of profound clarity. He accepts that his greed was, in its purest form, a deep-seated hunger for emotional bonds. In a heroic sacrifice, he turns his own ultimate defense against himself, converting his impenetrable carbon skin into brittle charcoal to destroy Father from the inside. With his final moments, he acknowledges his companions—Ling, Edward, and Alphonse—as the only things he ever truly wanted.

In terms of abilities, Greed is known as the "Ultimate Shield". His primary power is the ability to manipulate the carbon atoms in his body, rearranging them to form a layer of graphene or a diamond-hard lattice on his skin. This shield is nearly indestructible and can block bullets, blades, and even powerful alchemical attacks. He can harden his entire body or just specific parts, and his fingernails become razor-sharp claws capable of rending stone and steel. Like all homunculi, he possesses a powerful regenerative healing factor that allows him to recover from most wounds, including severed limbs and crushed skulls, using the Philosopher's Stone within him. However, this regeneration is not limitless; enough damage will deplete the souls within his Stone. His most notable weakness is that he cannot use his ultimate shield and his regenerative abilities at the same time, leaving him momentarily vulnerable if he chooses to heal. Furthermore, the shield's carbon structure can be chemically altered by a skilled alchemist, as Edward Elric demonstrated by transmuting Greed's hardened arm into a weaker, brittle form of carbon. After merging with Ling Yao, Greed's combat effectiveness is enhanced by Ling's exceptional martial arts skills and swordsmanship, making him a far more formidable and agile fighter than he was in his original body.