Wolfgang Grimmer is a freelance journalist and a former resident of the East German orphanage known as Kinderheim 511. His exact birth name and family origins are unknown, as he was placed in the orphanage as a young child and later given the name Wolfgang Grimmer by a state organization that trained him as a spy. Born in 1954, he is in his mid-forties during the main events of the story. Grimmer is a tall, thin man with short, messy sandy blonde hair, a prominent nose, and what are often described as honest brown eyes. He typically wears simple, comfortable clothing and is almost never seen without a large shoulder bag.

On the surface, Grimmer presents a personality marked by unusual cheerfulness and warmth, almost always greeting the world with a smile. He is gentle, helpful, and protective towards others, particularly children. However, this bright demeanor is a learned behavior, a direct consequence of the psychological reprogramming and severe abuse he suffered at Kinderheim 511. The experiments at the orphanage stripped him of his childhood memories and his ability to feel complex emotions such as sadness, joy, or love. Consequently, he has had to painstakingly learn appropriate emotional responses, often smiling in situations that would normally call for grief or anger. He has stated that "learning to smile was the hardest thing they taught me". Despite his internal emptiness, Grimmer possesses a strong moral compass and a deep, almost compulsive drive to protect others, which often motivates him to act with great selflessness.

His primary motivation is to uncover the truth about his own past and bring to justice those responsible for the horrors of Kinderheim 511, including the pedagogue Franz Bonaparta, whose theories were used in the orphanage's experiments. As a freelance journalist, he specializes in investigating human rights abuses and child welfare issues in the former Eastern Bloc. His role in the story becomes significant when he meets Dr. Kenzo Tenma, whom he helps escape across the border, recognizing Tenma's innocence simply by looking into his eyes, a skill honed from his years as a spy. Their paths continue to cross, and Grimmer becomes a crucial ally to Tenma, independently investigating the same dark conspiracy surrounding Johan Liebert and the former East German regime.

Grimmer's key relationships are defined by his quest. He forms a strong bond of mutual trust with Tenma, each recognizing a kindred spirit in their pursuit of justice. He also works closely with the young and idealistic Prague detective Jan Suk, protecting him and clearing his name. His past is marked by the tragic relationship with his ex-wife and son. While working as a spy under the guise of a journalist, he married a woman who confessed her love to him. Despite being unable to reciprocate genuine affection, he believed a family would provide better cover and did his best to be a good husband and father. The relationship fell apart after their young son died from an undiscovered medical condition. Unable to process the loss or feel any sorrow, Grimmer stood expressionless at the funeral, leading his wife to accuse him of having no heart and to divorce him.

The most notable aspect of Grimmer's character is his development regarding his own suppressed emotions. Throughout the series, he uses his logical and analytical skills to navigate situations where feelings are expected. However, in moments of extreme duress or life-threatening danger, he loses consciousness, and a violent, superhumanly strong alter-ego emerges, which he calls "The Magnificent Steiner" after a cartoon he vaguely remembers from his childhood. This personality is a manifestation of the rage and violent conditioning instilled in him at Kinderheim 511. When he awakens, he has no memory of the brutal acts committed by Steiner, whose power is shown to be capable of defeating multiple armed assailants. He deeply fears this side of himself and typically refuses to carry a gun, worried about triggering it. Over the course of the narrative, Grimmer undergoes a significant transformation. In a poignant moment, he is able to shed genuine tears while saving a traumatized boy named Milosz, marking the first time he consciously experiences a deep emotion. This evolution culminates in the town of Ruhenheim, where, after a young girl is killed, he consciously unleashes his rage. He fights and destroys a group of snipers to protect the remaining survivors, sustaining fatal injuries in the process. In his final moments, he weeps, finally able to feel the grief for his son and the joy of being human, asking if this is what true happiness is.

Grimmer possesses several notable abilities resulting from his training. He is a highly observant and resourceful individual, capable of quick thinking in crisis situations and often taking a leadership role. He can speak multiple languages, including German, English, French, Spanish, and Russian. His training as a spy has given him an exceptional ability to read people, discerning guilt or innocence almost intuitively. While he is capable of hand-to-hand combat and knows how to use a firearm, he prefers non-violent solutions, making his capacity for violence as the Magnificent Steiner all the more tragic and terrifying. The Magnificent Steiner form grants him superhuman strength and ferocity, capable of killing with his bare hands, making him one of the most physically dangerous characters in the story when this side is unleashed.