- “Longing. Rusted. Seventeen. Daybreak. Furnace. Nine. Benign. Homecoming. One. Freight car. Soldier? Mission Report December 16, 1991!”
- ―Baron Zemo
In the comics, the Zemo family were of German nobility, all of which were barons. However, Heinrich Zemo was allied with the Nazi organization H.Y.D.R.A., as a brilliant scientist yet a power-hungry aristocrat and supervillain with a grudge against Captain America, who he fought in World War II. His legacy was carried on by his son, Helmut Zemo, who formed the team of villains the Masters of Evil.
In the MCU, Helmut Zemo was a Sokovian soldier who lost his family during Ultron's attack on his country. Blaming the Avengers for his loss, he thus sought to tear them apart by staging a terrorist attack on the signing of the Sokovia Accords, setting off a chain of events that led to the Avengers fighting eachother and splitting up.
Marvel Animated Universe
Baron Heinrich Zemo was the leader of HYDRA during World War II. He used a more refined version of the Super Soldier Serum to enhance his natural physical abilities beyond Captain America's super-soldier limits, with even Captain America somewhat admitting his physical superiority. He once created Virus X and was stopped by Captain America, which resulted in the vial of virus falling on Zemo's face.
In present day, Zemo was jailed in the Raft and was witness of Graviton's awakening.
When Zemo finds out Captain America lives again, he gets Arnim Zola's help to keep Cap's new allies, the Avengers, busy with Doughboys while he faces Cap at Avengers' Mansion. Zemo almost defeats Cap if not for the intervention of Black Panther, who gives Cap his shield back. Zemo escapes, and finds Enchantress and Executioner with an offer to him.
When Wonder Man is absorbed by the Arc Reactor, Amora uses a spell to revive him, then she and Zemo offer to join them to defeat the Avengers. Days later, Zemo with his new allies found the Abomination wandering in the desert. After his new allies defeat Wasp, Zemo appears saying one less to defeat. Later at the Avengers Mansion, Zemo defeated Captain America with the help of Wonder Man. When Zemo was gloating over his victory over Captain America, Abomination reminded that two new Avengers were not in the mansion. Crimson Dynamo carried Black Panther along Zemo but this was part of the plan of the Avenger. After being defeated by the Avengers, Zemo remained with the firm conviction that he would dominate the world as Amora promised him.
After defeating the Norne Queen, Amora brings the Norne stones to Zemo as she promised him. Zemo asks what happened to Grey Gargoyle, she replied that he did not survive the battle. After getting the Norne stones Zemo was very confident in defeating the Avengers. He later defeated Thor with the help of the Enchantress. Thor tries to convince Zemo do not trust the Enchantress, but Zemo reveals that he never trust her, then he puts a collar on her and orders her to take control of the Asgard troops when they arrive on Earth. However, Zemo is defeated by Thor after the Asgardian hitting him with Mjolnir.
As the Amora began to take revenge on the Masters of Evil, Zemo accompanied by Wonder Man and the Abomination went to the Avengers Mansion for help. Later, Amora disguised as Chemistro infiltrated on the mansion to finally get revenge on Zemo. As Captain America (Skrull) decided not help him, he pulls out from his pocket a Norne stone to defend himself from the Enchantress. When the Avengers defeat Amora, Zemo orders Masters of Evil attack the Avengers so he can kill Amora. Wonder Man sick of Zemo's acts decides to betray him and prevents the Enchantress' death. Later, Zemo is defeated and taken to 42.
Baron Heinrich Zemo was seen in a flashback when he was fighting Captain America and Bucky Barnes. It is mentioned that he was imprisoned upon his defeat.
Baron Helmut Zemo was seen when he planned to finish his father's work into making an attempt at the super-soldier serum. In order to access it, he uses old-fashioned hypnosis to have Captain America re-enact his and Bucky's fight with his father Heinrich in order to find his lab. Using his attempt at a super-soldier serum, Helmut used it on two Hydra operatives, turning them into large brutes. He ended up injecting himself with one of his father's super-soldier serums, effectively euthanizing himself as well gaining as superhuman strength and speed. After this occurred, Helmut engaged Iron Man and Black Widow in battle. After the illusion of Bucky snapped him out of his hypnosis, Captain America joined the fight against Helmut. When the cliff the fight occurred on gave way, Helmut refused Captain America's offer to save him and fell into the ocean to retrieve the last of his father's super-soldier serum. Iron Man's computers could not detect Helmut under the surface of the ocean.
Zemo later resurfaces as the superhero Citizen V, helping the Avengers defeat Growing Man. Originally, his plan was teaming up with the Masters of Evil, and disguising them as a new superhero team called the Thunderbolts. However, when their secret was exposed, the Avengers and Masters were left to die in a collapsing warehouse while Zemo as Citizen V gained public sympathy from their deaths. However, the Avengers and the Thunderbolts, now genuinely reformed, exposed his true identity to the city, foiling his plan. Initiating a backup plan, Zemo unleashed a supercharged Ulysses Klaw against them, while he escaped.
After obtaining leftover time travel technology from Kang the Conqueror, Zemo constructed a time portal to make contact his father, Heinrich Zemo, the original Baron Zemo. He eventually was able to bring his father from the 40s during World War II to the present day, just as Captain America, Falcon and Black Widow arrived. Heinrich resolves to strand the three Avengers in his own time period, forcing them into the portal. During the fight between the Avengers and the Zemos, Heinrich started to see Helmut as a disappointment enough to use the time machine to bring forward a Zemo from the year 2099. After Helmut got trapped under some debris, his own father declined to help him. After being freed from the debris from Captain America, Helmut worked with Captain America to send Heinrich back to 1943 which also erases Zemo 2099's existence. As Helmut had cooperated with Captain America, he won't be sent to the Vault. Baron Zemo next appears in Avengers: Secret Wars. Zemo has a confrontation with Black Panther and Ant-Man while obtaining a Wakandan relic hidden away by T'Chaka and Heinrich. Despite being empowered by the hidden relic (to the point of insanity), he is defeated by the two members of the New Avengers.
Colonel Helmut Zemo is a Sokovian citizen and a terrorist who sought revenge against the Avengers after losing his family during the Battle of Sokovia, becoming obsessed with defeating and destroying them. Knowing that he's no match against the Avengers, he instead planned to have them destroy each other by first framing the Winter Soldier for the assassination of T'Chaka, causing Captain America to defend his friend from the world. This action caused the Avengers Civil War in which Iron Man led a man-hunt for the Winter Soldier and Zemo allowed Iron Man to discover that the Winter Soldier was also responsible for the deaths of his mother and father. With the Avengers in ruins, Zemo explained his motives to Black Panther, who was about to kill him after learning the truth about his father's death, but stopped after realizing how much vengeance had consumed him. Zemo attempted to commit suicide but was stopped by Black Panther and handed over into the custody of Everett Ross for his imprisonment.
- In the comics, there are two versions of Baron Zemo. The first, Heinrich Zemo, was the enemy of Captain America during World War II. The second, Helmut Zemo, is Heinrich's son who succeeded his father's villainous career in opposing Captain America.
- In the comics, Zemo's father Heinrich developed a serum called Adhesive X, an extreme form of superglue (as noted by Black Widow) which after accidental exposure became the reason Heinrich never took off his hood. Later on in his life, Helmut was exposed to the serum as well, disfiguring him, though it doesn't appear to be the in-show reason for why they never showed his full face after his reaging and empowerment.
- The Baron Zemo in The Avengers: Earth's Mightiest Heroes is Heinrich Zemo, but with some traits of Helmut Zemo, like his present-day appearance and his swordsmanship ability. In Avengers: Ultron Revolution, both versions of Zemo appear exactly as they had in the comics.
- As opposed to the comic versions of Baron Zemo, who was a supervillain and had varying degrees of superhuman abilities as seen in The Avengers: Earth's Mightiest Heroes and Avengers Assemble, the one in Civil War has no super-powers or swordsmanship skills, but is a master of manipulation and military strategy.