Sin's journey into the Marvel Universe is a multi-stage evolution, reflecting the changing tones of comics over the decades. Her first chronological appearance was as a child, Sinthea Schmidt, in Captain America #290, published in February 1984. She was created by the celebrated writer J. M. DeMatteis and artist Paul Neary. In this initial incarnation, she was introduced as the young leader of a group of psychically-powered girls called the Sisters of Sin, operating under the villainous moniker Mother Superior. This version of the character was more mystical and less of a direct physical threat. The character lay dormant for many years until she was radically reimagined and reintroduced into modern continuity by writer Ed Brubaker and artist Steve Epting. This modern, far more menacing version of the character, now known as Sin, made her debut in Captain America (vol. 5) #21 in October 2006. Brubaker's tenure on Captain America is widely regarded as one of the title's definitive runs, and his decision to resurrect Sinthea Schmidt was a masterstroke. He stripped away the more fantastical elements of her past, grounding her as a brutal, psychologically damaged terrorist and the perfect field operative for her father's grand schemes. This transformation was instrumental in shaping the “The Death of Captain America” storyline, cementing Sin as a major, A-list villain in Marvel's hierarchy.
The origin of Sin is a tragic and horrifying tale of abuse, indoctrination, and twisted legacy. Her history is one of the darkest in Marvel Comics, defined entirely by the monstrous ambitions of her father.
Sinthea Schmidt was born in the 1940s on Skull-House, a private island owned by her father, Johann Shmidt, the original Red Skull. The Red Skull, obsessed with creating a perfect male heir to carry on his legacy, was disgusted upon learning he had a daughter. He was prepared to murder the infant on the spot, but his follower, Susan Scarbo (later known as the manipulative psionic villain Mother Night), convinced him that the child could still be of use. The Red Skull agreed, but refused to raise the child himself. Instead, Sinthea was raised by Mother Night, who subjected her to a brutal and unforgiving upbringing steeped in the Red Skull's nihilistic and hateful ideology. From her earliest moments, she was taught that HYDRA was her family, hate was her strength, and her father was a god. To accelerate her use as a weapon, the Red Skull placed Sinthea into a special machine that artificially aged her body to adulthood, though her mind remained dangerously immature and impressionable. Now an adult in form, she was dubbed Mother Superior. With her psionic abilities enhanced, she was made the leader of the Sisters of Sin, a group of young orphan girls who were similarly brainwashed and empowered. As Mother Superior, she clashed with Captain America multiple times, but was eventually captured by S.H.I.E.L.D.. Recognizing she was a victim, S.H.I.E.L.D. reversed the aging process, returning her to her proper chronological age as a young girl, and used psychological techniques to block her traumatic memories. She was adopted into a normal family and given the name Erica Holstein, completely unaware of her terrifying past. Years later, the sociopathic mercenary Crossbones, one of her father's most loyal lieutenants, was tasked with finding her. He located the teenage Erica, kidnapped her, and subjected her to intense physical and psychological torture. He systematically broke S.H.I.E.L.D.'s mental blocks, forcing her to remember her life as Sinthea Schmidt. The process was a brutal success. Not only did her memories return, but they were twisted into a fanatical devotion. Erica Holstein was gone, and in her place stood Sin, a reborn killer loyal to her father and in love with the man who “freed” her, Crossbones. Her transformation was physically completed during a confrontation with the new Captain America, Bucky Barnes. As she prepared to kill him, Bucky threw the shield, which grazed the side of her face, horribly disfiguring her. The scarring gave her a skeletal, skull-like visage, making her a true physical heir to the Red Skull. This moment crystallized her hatred for Bucky Barnes, a hatred that would burn even more intensely than her inherited disdain for Steve Rogers.
Sinthea “Sin” Schmidt does not exist in the Marvel Cinematic Universe. Her character, history, and impact are entirely confined to the comic book continuity. The MCU's narrative for her father, Johann Schmidt, makes her existence highly improbable within the established timeline. In Captain America: The First Avenger, the Red Skull is transported across space by the Tesseract (the Space Stone) in 1945. As revealed in Avengers: Infinity War and Avengers: Endgame, he was not killed but cursed to become the ethereal Stonekeeper on the planet Vormir, guarding the Soul Stone. He remained there for over seven decades until Thanos arrived. This narrative effectively removes the Red Skull from Earth during the entire period when he would have fathered and raised Sinthea in the comics. There was no opportunity for him to have a child, build a new HYDRA, or create the Sisters of Sin. While HYDRA continued to operate secretly within S.H.I.E.L.D., it was under the leadership of figures like Arnim Zola and later Alexander Pierce, not a physically present Red Skull. Theoretically, a version of Sin could be introduced in the future MCU, but it would require a significant retcon or a complete reimagining of her origin. Possible avenues could include:
As of now, however, any discussion of Sin in the MCU is purely speculative.
Sin's threat level is a potent combination of inherited intellect, ruthless training, and sheer force of will. While she lacks innate superhuman powers for most of her history, she is one of the most dangerous non-powered humans on Earth-616.
Sin is the personification of her father's ideology. She is a true believer in the doctrine of hate, chaos, and nihilism. Her personality is defined by:
During the Fear Itself event, Sin was temporarily transformed into Skadi, one of the “Worthy,” after lifting the enchanted Hammer of Skadi. In this form, she possessed immense superhuman powers on an Asgardian scale:
Sin utilizes a vast arsenal of weaponry, combining conventional tools of terror with HYDRA's advanced technology. This includes customized firearms, high-explosives, combat knives, and access to HYDRA's vehicles and super-weapons.
As Sin does not exist in the MCU, she possesses no established abilities, personality traits, or equipment within this continuity. Should a character inspired by Sin ever be introduced, it is likely she would mirror her comic counterpart's role as a non-superpowered threat. She would be portrayed as a master hand-to-hand combatant, expert tactician, and ruthless terrorist leader, filling the void for a charismatic and ideologically-driven HYDRA commander in the post-Winter Soldier era. Her skills would be grounded in espionage and military training rather than superpowers, making her a formidable and personal threat to characters like Sam Wilson's Captain America or Bucky Barnes.
Sin's identity is defined by her relationships, nearly all of which are built on a foundation of conflict, control, and violence.
Sin's modern character arc is defined by her central role in some of Marvel's most significant events of the 21st century.
This storyline is Sin's defining moment. Following the superhero Civil War, the Red Skull enacts his master plan to assassinate Steve Rogers. Sin serves as his primary field commander, working alongside Crossbones to execute the intricate plot. While Crossbones acts as the sniper to distract the authorities, it is a brainwashed Sharon Carter, manipulated by Doctor Faustus, who fires the fatal shots. Sin's role was to manage the operation on the ground, personally engaging with S.H.I.E.L.D. agents and ensuring the plan succeeded. In the aftermath, she and her crew are relentless in their pursuit of Bucky Barnes and the Falcon, cementing her as the new face of Captain America's rogues' gallery.
It is revealed that Steve Rogers was not killed, but frozen in time, unstuck in his own past. The Red Skull, now inhabiting a robotic body, devises a scheme to use a captured Sharon Carter and technology created by Arnim Zola to bring Steve back to the present, but with the Skull's own consciousness in control of his body. Sin is once again a key player, fighting alongside her father's forces against the Avengers to ensure the plan's success. Her fanatical drive to see her father “reborn” in the body of his greatest enemy highlights the depths of her psychological devotion.
This event elevated Sin from a street-level terrorist to a global, cosmic-level threat. Seeking a weapon of ultimate power, she travels to a secret HYDRA facility in Antarctica where she discovers the Hammer of Skadi, one of seven mystical weapons unleashed upon the Earth by the Serpent. Upon lifting it, she is transformed into Skadi, the Serpent's herald and the first of his Worthy. Wielding immense power, she leads a massive assault on Washington, D.C., and engages in a brutal battle with Bucky Barnes. In a shocking moment, she seemingly kills Bucky, demonstrating her new god-like power and achieving a personal, bloody victory over one of her most hated foes. Though Bucky's death was faked using a Life Model Decoy, the event solidified Sin's status as a major threat to the entire Marvel Universe.
Unlike many major Marvel villains, Sin does not have a wide array of prominent alternate-reality counterparts, which underscores how integral she is to the specific, modern history of the Earth-616 Captain America.