Van Hohenheim is a deceptively ancient and extraordinarily powerful alchemist who serves as the estranged father of Edward and Alphonse Elric. His history begins centuries before the main events of the story in the ancient kingdom of Xerxes, where he lived as an illiterate slave known only by the number twenty-three. His life changed forever when a homunculus living inside a flask was created using Hohenheim's blood. As a gesture of gratitude, this creature gave the slave the name Hohenheim and proceeded to teach him how to read, write, and practice alchemy. The homunculus later convinced the King of Xerxes to perform a massive transmutation circle under the guise of granting immortality. When the circle was activated, every citizen in the country was sacrificed to create a massive Philosopher's Stone. The homunculus took half of those souls to form its own body, becoming the being known as Father, while the other half of the souls were forced into Hohenheim's body, transforming him into a living Philosopher's Stone. Despite containing over five hundred thousand souls within himself, Hohenheim dedicated years to speaking with each one, helping them overcome their madness and suffering.

In terms of personality, Hohenheim initially appears as a cold or distant figure, which is largely a result of his difficulty in communicating and the immense burdens he has carried for centuries. He is generally gentle, weary, and soft-spoken, reacting with remarkable calm even when his son Edward punches him in the face. He can be prone to making foolish statements, is immune to embarrassment, and tends to speak in cryptic ways while occasionally testing the character of those he meets. He possesses a compassionate and pacifistic nature, remaining humble and never accepting compliments for himself. His long life has given him a perspective that makes him appear detached at times, but this masks a deep-seated guilt and a genuine desire to protect others. He lacks the obsessive drive that characterizes his son Edward, and in his youth was a person without ambition who would have been content with a simple life.

Hohenheim's primary motivation throughout the story is to stop Father's plan to use the entire nation of Amestris as a sacrifice to create another Philosopher's Stone and achieve the power of a god. After discovering this plot, he left his beloved family in Resembool, understanding that his sons would grow to hate him for his absence but accepting this as necessary to save their lives and the lives of everyone in the country. Beneath this heroic goal lies a more personal desire. Having finally found true love with his wife Trisha Elric, Hohenheim desperately wanted to become mortal again so that he could grow old and die alongside his family. He spent years searching for a way to achieve this. His love for Trisha, whom he considered the only woman he ever truly loved, stands in stark contrast to his previous centuries of aimless existence.

In the broader narrative, Hohenheim operates largely behind the scenes for much of the series, but his actions prove crucial to the final outcome. He spent years traveling across Amestris, secretly placing fragments of his own Philosopher's Stone at key points throughout the country. When Father finally activated the nationwide transmutation circle on the Promised Day, Hohenheim activated his own counter-circle, which reversed the effect and returned the souls of every Amestrian citizen to their bodies, saving countless lives. He directly confronted Father, attempting to settle matters peacefully before violence became necessary, and later shielded Izumi Curtis and Edward from a lethal blast by using his own body. Ultimately, he offered up his own body to be used as material for Edward to bring Alphonse back from the Gate of Truth.

Hohenheim's key relationships are defined by tragedy and reconciliation. His relationship with Father is the most significant, as Father was created from his blood and was once his teacher and companion. The two share an identical appearance and an understanding of what it means to be living Philosopher's Stones, yet they stand as philosophical opposites. While Father seeks to transcend humanity and discard all emotion, Hohenheim cherishes human connection and feels profound guilt over the deaths that granted him immortality. In the end, Hohenheim even feels sympathy for Father, understanding his desire for freedom and being saddened by his death. His relationship with his sons, particularly Edward, is initially hostile due to his long absence. Edward resents him for abandoning the family and for not being present when Trisha died. However, as the truth of Hohenheim's mission becomes clear, Edward begins to understand his father's sacrifices. When Edward finally relays Trisha's dying words, Hohenheim breaks down in tears, and a genuine reconciliation begins. His relationship with his wife Trisha forms the emotional core of his character, as she was the only person who knew what he truly was and accepted him anyway, giving him a reason to love life after centuries of loneliness. Upon learning that his sons are safe and healthy after the final battle, he leaves in tears of gratitude and eventually dies peacefully at Trisha's grave, finally reunited with her in death.

Hohenheim possesses abilities that make him one of the most powerful alchemists in the series. As a living Philosopher's Stone, he has access to vast amounts of energy that allow him to perform transmutations without a conventional circle and with far greater power than ordinary alchemists. His body can instantly regenerate from any injury, as demonstrated when he was shot multiple times by bandits and stood up completely unharmed. He has studied alchemy for several centuries, making him exceedingly learned in its applications. His nickname, Hohenheim of Light, comes from his ability to transmute light itself. Only Father is capable of rivaling his power. Despite his immense strength, he prefers peaceful solutions and uses his abilities primarily to protect others and counter Father's plans rather than for direct combat. His greatest feat of alchemy was the creation of a nationwide counter-transmutation circle that saved the entire population of Amestris from being turned into a Philosopher's Stone.

Throughout his development, Hohenheim transforms from a figure shrouded in mystery and presumed irresponsible into a tragic hero whose centuries of solitary wandering and suffering were undertaken entirely for the sake of others. He begins as an immortal being who had resigned himself to an endless existence without purpose. Meeting Trisha and having children gives him a new perspective and a desperate wish to become mortal. His apparent abandonment of his family is reframed as an act of supreme self-sacrifice, leaving the people he loved most to save them from a threat they could not comprehend. By the end of his life, he achieves his goals. Father is defeated, the nation is saved, and he reconciles with his sons. Having finally fulfilled his purpose, he allows himself to die, having lived long enough to hear Edward call him father for the first time with genuine affection. His final moments, spent at Trisha's grave, represent the peaceful end he had sought for centuries.