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 defeat 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 Mjonir.
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. 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 Zemo 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 youthanizing himself as well gaining as superhuman strength and speed. After this occured, Zemo 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 Zemo. When the cliff the fight occured on gave way, Helmut Zemo 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 Zemo under the surface of the ocean.
Zemo later resurfaces as the superhero Citizen V, helping the Avengers defeat Growing Man.
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.
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 & military strategy.
Zemo will be a member, possibly the leader, of the super villain team, the Masters of Evil. Both Heinrich and Helmut Zemo led several iterations of the Masters in comics and other media.
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.