Created by writer Stan Lee and artist Don Heck, the character first appeared in Journey into Mystery #99 (December 1963).

[6] Calvin Zabo debuted in Journey into Mystery #99 (December 1963), created by Stan Lee and Don Heck.

Calvin Zabo was born in Trenton, New Jersey and becomes a morally abject but brilliant biochemist who discovered the effects of hormones on human physiology.

He convinced himself that the experiment Dr. Jekyll performed in the story could actually be accomplished and became obsessed with the idea of unleashing his full bestial nature in a superhuman form.

Though too intelligent to be caught, the medical community became suspicious, due to his tendency of always getting employed by organizations which were subsequently robbed.

He eventually became successful in creating his formula and turned himself into a massive, Hulk-like creature he called Mister Hyde, named after the character in the story.

In this new form, Hyde found out he had immense strength allowing him to crush cars and tear through steel as though it were made of cardboard.

[15] While serving in prison following this failed attempt, Hyde was ensnared by the mind-control power of the Purple Man, and forced to battle Daredevil in an arena alongside Cobra, Jester, and Gladiator.

[16] Tiring of their repeated failures, the Cobra elected to sever their partnership when he escaped from Ryker's Island, taking the time to taunt Hyde before leaving.

[21] Hyde later became a member of Helmut Zemo's incarnation of the Masters of Evil and invaded Avengers Mansion along with them, torturing the Black Knight and Edwin Jarvis.

[22] Hyde later attempted an escape from the Vault alongside Titania, Vibro, Griffin, and Armadillo, but was defeated and recaptured by the Captain.

[26] He was subsequently caught by the police when he coincidentally checked into the same hotel as the one where the Daily Bugle staff were attending Robbie Robertson's retirement party, allowing Peter Parker to defeat him using an improvised costume.

[29] Zabo was being held in the Raft (the Ryker's Island Prison complex) six months after the events of "Avengers Disassembled.

"[30] When a prison break was caused by Electro, Zabo emerged in his Hyde persona, fought with Daredevil, and was knocked unconscious by Luke Cage.

[31] At one point, Zabo was discovered by the Young Avengers to be selling a derivative of his Hyde formula on the street as one of the various illegal substances known as Mutant Growth Hormone.

; her mother was apparently a sex worker whose services Calvin Zabo frequented and the girl was put up for adoption after birth.

[34] The Hood hired him as part of his criminal organization to take advantage of the split in the superhero community caused by the Superhuman Registration Act.

[36] Hyde worked with Boomerang, Tiger Shark, and Whirlwind to manipulate Venom into procuring Norman Osborn's fortunes.

This was thwarted by Venom and Green Goblin as Osborn threw a bomb into Hyde's mouth, causing him to spit out blood.

Robbie is revived as a demonic being called the Ghost Rider and defeats Zabo, becoming something of a local hero and urban legend.

[50] The process that transforms Calvin Zabo into his Mister Hyde persona are growth hormones caused by ingestion of a chemical formula.

He employs a wristwatch-like device supplied with the formula that injects itself directly into his bloodstream, thus enabling to transform himself by button pushing.

In the end, Daredevil uses his past friendship with Dent to talk Two-Face into supplying the antidote for the chip, which saves Hyde's life.

[58] Before the Red Guard attacks Santo Rico, Hyde leaves the team alongside the Cobra, Crossbones, and Thunderball.