Alphonse Elric is the younger brother of Edward Elric, and together they serve as the central characters of their story. Born in the rural town of Resembool, Alphonse had a fairly typical childhood until his mother Trisha passed away from an illness, leaving him and his brother in the care of their neighbors, the Rockbell family. Their father, Hohenheim, had already left home years earlier and was not present during this time. In a desperate attempt to bring their mother back to life, Alphonse and Edward, who had been studying alchemy from a young age, committed the ultimate taboo of human transmutation. The attempt was a catastrophic failure. As a toll for opening the Gate of Truth, Alphonse lost his entire physical body. In a desperate act to save him, Edward sacrificed his right arm to bind Alphonse's soul to a large suit of armor. This binding is maintained by a blood seal drawn on the inside of the armor's neck, meaning that if this seal is ever completely damaged or erased, Alphonse will cease to exist.

In stark contrast to his often hot-headed and impulsive older brother, Alphonse possesses a calm, gentle, and deeply compassionate personality. He is soft-spoken and polite, frequently acting as the voice of reason and the moral compass for the duo. He has a particular fondness for stray animals, often trying to take in abandoned cats, much to Edward's annoyance. Despite his gentle nature, Alphonse is not without a temper; when pushed too far, he can display a fierce stubbornness and determination that matches his brother's own. He is also incredibly selfless, often putting the well-being of others before his own. While he is generally more emotionally stable than Edward, he is not immune to doubt, and early in their journey, he grapples with a profound existential crisis, fearing that he might merely be a construct of his brother's alchemy with false memories.

Alphonse's primary motivation is to regain his original body and to restore his brother's lost limbs, though he consistently insists that Edward's well-being is just as important as his own. He feels a sense of shared responsibility for the taboo they committed and is driven by a desire to atone for their actions. Throughout their journey, he also becomes motivated to protect innocent people from the horrors created by the Philosopher's Stone and the machinations of the homunculi. He holds onto a quiet but unshakable hope that they can undo the mistake of their past without causing further harm.

In the story, Alphonse serves as both Edward's protector and his anchor. His imposing suit of armor makes him a formidable fighter, often taking hits that would be fatal to his brother. Conversely, his emotional intelligence helps to ground Edward, preventing him from being consumed by his own guilt and rage. The brothers are almost inseparable, and their relationship is the emotional core of the narrative. They share a deep, unbreakable bond, having seen the worst of alchemy together and vowing to make it right. He also shares a strong bond with Winry Rockbell, their childhood friend and Edward's automail mechanic, who acts as a sisterly figure and a tether to their old life in Resembool. He trains under the严厉 tutelage of Izumi Curtis, who becomes a surrogate mother to both brothers. Throughout the series, he also forms key alliances with characters such as the Xingese prince Ling Yao and the chimera Heinkel, who aid him in critical moments.

Over the course of the series, Alphonse undergoes significant development. He begins as a somewhat passive follower of his brother's lead but gradually grows into a more independent and decisive individual. His crisis of identity, where he fears his memories and soul are artificial, is a major turning point, after which he emerges with a stronger sense of self. When his ally Martel is killed while inside his armor, her blood splashes onto his blood seal, giving him a near-death experience that allows him to recall his time at the Gate of Truth. This event restores his memory of that moment and grants him the ability to perform alchemy without a transmutation circle, a skill previously unique to those who had seen the Truth. As the story reaches its climax, his soul begins to show signs of rejection from the armor, indicating that his time in that form is limited. In the final battle, his armor is critically damaged. To save Edward, he has Mei Chang use his soul as the currency to transmute back Edward's right arm, seemingly sacrificing himself. Ultimately, Edward uses his own ability to perform alchemy as the final toll to restore Alphonse's soul to his original, living body.

As an alchemist, Alphonse is exceptionally talented. He is well-versed in the theory and practice of alchemy, though his approach is often more methodical and by-the-book compared to Edward's intuitive genius. After regaining his memories of the Gate, he can transmute without a circle simply by clapping his hands, just like his brother. His combat style is heavily augmented by his armor. He is a skilled hand-to-hand fighter, having trained with Izumi Curtis, and his metal body makes him extremely durable, immune to pain, and capable of powerful physical strikes. The armor also makes him resistant to most conventional weapons and environmental hazards, though it leaves him unable to experience physical sensations like taste or touch and renders him unable to swim for fear of the blood seal dissolving. While he possesses great power, he is also a creative alchemist, able to transmute the environment and even his own armor's composition to gain an advantage in battle.