Alphonse Elric, often called Al, is the younger brother of Edward Elric and the secondary protagonist of the story. Born in the rural town of Resembool, Al was the younger son of the alchemist Van Hohenheim and Trisha Elric. After his mother died from an illness and his father had already left home, a young Al and his brother Edward devoted themselves to the study of alchemy, driven by the desire to see their mother's smile again. This pursuit led them to the forbidden human transmutation, an attempt to bring Trisha back to life. The attempt failed catastrophically. As the toll for breaking the ultimate taboo, Al lost his entire physical body. In a desperate act to save him, Edward sacrificed his right arm to perform a second transmutation, binding Al's soul to a large suit of armor by inscribing a blood seal on the inside of its neck.

As a result, Al exists as a soul attached to a hollow suit of armor. He cannot feel physical sensations, taste food, or sleep, and his continued existence depends entirely on the preservation of the blood seal on the armor's interior; if it is damaged, he will die. He also cannot swim, as the pressure and water could damage the seal. Despite this tragic circumstance, Al is the emotional anchor of the Elric brothers. He is defined by his gentle, compassionate, and kind-hearted nature, a stark contrast to his older brother's hot-headed and impulsive personality. Al possesses a deep, almost maternal, love for living things, often picking up stray cats and hiding them inside his armor, much to Edward's exasperation. He is polite, patient, and rarely raises his voice, serving as the voice of reason who frequently has to restrain Edward from acting recklessly. However, this gentleness does not equate to weakness. Edward himself has stated that Al has never lost a fight between them, and his quiet resolve and inner strength are formidable.

Al's primary motivation is, alongside his brother, to restore his original body. He deeply misses the simple human experiences of warmth, touch, and taste. Yet, his motivations are never purely selfish. He is driven by a powerful sense of justice and empathy, wishing to prevent others from suffering the same pain he and Edward have endured. After witnessing tragedies like the fate of Nina Tucker, he resolves to stop those who would misuse alchemy for cruel purposes. He is incredibly selfless, and the thought of using the Philosopher's Stone, an object made from human souls, to restore his own body is abhorrent to him. His role in the story is that of a crucial partner to Edward. While Ed is the recognized Fullmetal Alchemist who often devises plans and fights on the front lines, Al is the steadfast support, both in combat and in emotional resilience. His imposing armor often leads strangers to mistake him for the Fullmetal Alchemist, a recurring joke that irritates his shorter brother.

Throughout the journey, Al's key relationships are the foundation of his character. His bond with his brother Edward is the most important. It is a relationship of profound love, mutual sacrifice, and at times, conflict, such as when Al briefly doubted whether he was a real person or a fabricated copy. His teacher, Izumi Curtis, is another mother figure who taught him not only alchemy but the philosophical principle of "one is all, and all is one," shaping his understanding of life and sacrifice. Winry Rockbell, their childhood friend and eventual sister-in-law, is a source of support, and he maintains a close friendship with her. He also forms a significant bond with the young Xingese princess May Chang, who is initially drawn to him mistaking his armor for the mythical "Living Philosopher's Stone." Their relationship grows into a deep mutual respect and, in the end, a romantic one.

Alphonse undergoes significant development. Initially, he cannot perform alchemy without a transmutation circle because the trauma of the failed human transmutation caused him to forget his experience at the Gate of Truth. However, after a near-death experience when the blood seal is touched, he regains his memories and the ability to perform alchemy without a circle, a sign of having seen the Truth. His internal struggle also evolves. He grapples with feelings of being a burden to Edward and with the terrifying uncertainty of his own existence as a soul bound to metal. In the final battle, his development culminates in a moment of ultimate selflessness. With his armor critically damaged, he uses his own soul as a bargaining chip to trade for the return of Edward's right arm, allowing his brother to defeat the final antagonist. It is only then that Edward, in turn, sacrifices his own ability to perform alchemy to restore Al's original body, bringing his character arc to a complete and emotional close.

In terms of abilities, Al is a highly skilled alchemist. Trained in the brutal but effective methods of Izumi Curtis, he is a master of hand-to-hand combat, often using his heavy armor body to deliver powerful, unarmed strikes. His alchemy is precise and practical, used to create weapons, shields, and alter the terrain to his advantage in battle. Before regaining his memories, he was reliant on drawn circles, but later he gains the ability to transmute with just a clap of his hands, like his brother. Despite not having muscles, his armored body grants him immense durability, making him impervious to bullets and able to withstand powerful blows, though this invulnerability is always balanced by the fragility of his blood seal.