In order to finance his incredibly expensive research, Zabo systematically robbed his various employers. He managed to avoid criminal prosecution by changing employers often. However, his bad reputation caught up with him. Zabo applied for work with a noted surgeon, Dr. Donald Blake (alias Thor), but was refused employment based on his past misdeeds. Zabo became furious and vowed vengeance upon the lame doctor. Calvin Zabo then turned his full attention to his research.

Several months later, Zabo discovered the formula to transform himself into Mr. Hyde. The chemical process is hormonal in nature, causing the cells of his anatomy to instantly manufacture mutated hormones that induce a physical transformation encompassing his entire figure. Miraculously, over 200 pounds of bone and muscle tissue are added to Zabo’s body. After about 30 seconds, the entire metamorphosis is complete.

The transformation is excruciating. As his form mutates, Zabo’s skin is forced to stretch over his growing body. This distortion alters all of his physical characteristics. Hyde and Zabo have different finger prints, while Hyde’s facial structure is distorted to the point that he is frozen in a perpetual sneer. Zabo’s personality is also distorted. As Hyde, he is overcome with savage anger and bestial ferocity.

Hyde chose Dr. Donald Blake to be the first to suffer his wrath, but was defeated. In addition to Thor, his enemies include Captain America, Daredevil, Spider-Man, and especially the Cobra, a former partner who betrayed Hyde by leaving him to rot in prison. The Cobra is also the only person to know that Mister Hyde is actually Calvin Zabo.

On one occasion, Spider-Man had just captured the Cobra, when Hyde attacked, wanting revenge against his ex-partner. After a long and ferocious battle, Spider-Man defeated Hyde by knocking him out a high window, causing him to plummet to the street below. The indomitable Mister Hyde was not killed, but merely stunned. He and the Cobra were then easily captured and taken into police custody.

During his long career, Mister Hyde has also teamed up with Batroc the Leaper. They succeeded in hijacking a Roxxon super-tanker and capturing Captain America, whom they chained to the prow of the ship. The tanker was filled with 50,000 tons of liquefied natural gas. As it cruised through the harbor, Batroc and Hyde set it on a collision coarse with the docks of New York City. The resulting explosion would likely lead to the total destruction of the entire metropolis.

Batroc only wanted a huge ransom for the ship and Captain America. Hyde, however, wanted to go through with the plan, and cared nothing for the money: he simply wanted Cap and the rest of New York City’s population dead. When Batroc realized this, he secretly loosened the chains holding Captain America, who freed himself and dove into the harbor.

As Hyde was busy steering the ship, Batroc attacked him from behind. The former partners began a fight to the death. As Hyde began to squeeze the life out of Batroc, Captain America boarded the ship and attacked Hyde. During the fight, Hyde broke a pipe and was hit by a high-pressure stream of liquefied gas. Covered by a thick coating of the freezing liquid, Hyde fell over the side and sank in the harbor. Captain America tried to find him, but Hyde was gone. Cap caught Batroc, who tried to escape during the confusion, and returned the super-tanker to Roxxon officials.

Mister Hyde survived his encounter with Captain America and Batroc, and later joined with the Masters of Evil IV, whose members included Absorbing Man, Baron Helmut Zemo (the leader), Blackout, Goliath, Grey Gargoyle, Moonstone, Screaming Mimi, Tiger Shark, Titania, Whirlwind, the Wrecking Crew, and Yellowjacket.

While the Avengers were away, Baron Zemo and his Masters of Evil broke into Avengers’ Mansion and captured Jarvis, the butler. The Baron’s plan was then to capture the Avengers one-by-one as they returned to headquarters from their various errands.

They quickly captured the Black Knight and Captain Marvel. The Wasp, Captain America, and Hercules realized something was up inside their headquarters. Wasp and Cap wanted to wait and investigate the situation, but Hercules would have none of that, and he rashly charged into the building. He was immediately attacked by the majority of the Masters of Evil, and savagely beaten. Captain America tried to enter the mansion to help his ally, but was captured by the building’s own defense systems. The Wasp managed to escape.

Baron Zemo now had Jarvis, the Black Knight, and Captain America as hostages. He turned them over to the cruel hands of Mister Hyde, who started beating the butler to death. Hyde was having great fun, until the Wasp, Thor, Ant-Man, Doctor Druid, and Captain Marvel all arrived to help their friends. Hyde found himself heavily outmatched, and he was knocked unconscious by Thor. The rest of the Masters of Evil were subsequently defeated.

Most recently, Calvin Zabo was having a drink in a Manhattan bar, and recovering from a head wound given to him by the Hulk that prevented him from transforming into Hyde, when he insulted a waitress. The huge leader of a biker gang saw the incident, and he threw Zabo out of the bar. Determined to have revenge, Zabo re-entered the bar and hit the biker over the head with a bottle. This time Zabo threw himself out the window in an attempt to escape the enraged bikers. Zabo fled to a nearby parking garage and hid.

Meanwhile, Dan Ketch (alias the Ghost Rider) arrived at the garage, where he planned to store his motorcycle for a while. The attendant, Jack, happened to be a friend of Dan’s. As Dan and Jack talked, the angry bikers rolled into the garage. When Jack refused to let them pass, the bikers attacked. Dan and Jack were subdued and locked in the attendant’s office.

As the bikers searched for him, Calvin Zabo strained to overcome his head wound and transform into Hyde. He succeeded, at the same time Dan Ketch transformed into the Ghost Rider. Mister Hyde attacked the leader of the gang, and was about to smash a car full of innocent teenagers, when the Ghost Rider interfered. When Hyde met the Ghost Rider’s Penance Stare, he began to transform back into Zabo, then fled. The Ghost Rider rammed Hyde with his motorcycle, and both of them went flying out of the garage onto the street below. As the police arrived, both Hyde and the Ghost Rider vowed revenge, then went their separate ways.