The Birth: Inspired by the fictional tale of Doctor Jekyll and Mister Hyde, Calvin Zabo became obsessed with distilling the essence of human savagery. To facilitate his bizarre research, he stole money and equipment from his various employers. The cunning Zabo moved from job to job frequently and never left any firm evidence that could convict him, but his shady reputation eventually led Dr. Don Blake (secretly the thunder god Thor) to reject his application for employment. Incensed, Zabo vowed revenge and soon completed his "Hyde formula." Ingesting the mixture, Zabo was transformed into the superhumanly powerful and irredeemably evil Mister Hyde.
His first appearance was in Journey Into Mystery #99.

The Alter Ego: Dr. Calvin Zabo may be a genius in controlling human feelings of good and evil but, nevertheless, he is a loon. And a thief. A person with no scruples whatsoever.

The Legend: After his first transformation into Mister Hyde, he kept his vow to take revenge on Dr. Don Blake. He ended up battling Thor, the norse God of Thunder. While he has tackled Thor on many occassions, his most persistent foe has been Daredevil. Other heroes who he's tangled with are Spider-Man, Captain America, Falcon, Hulk, The Avengers and Ghost Rider. He has had a long time partership with the evil Cobra - a partnership that went sour when Cobra abandoned Zabo during a prison escape and earned Hyde's wrath. Since then Hyde has been after Cobra's life. In one attempt to destroy Cobra, Hyde found himself slugging it out with Spidey. In anouther attempt, he tried to blow up New York City but was foiled by Cap. Hyde has had quite a few other partnerships but they lasted for the fact that he would always turn on them or vice versa. Displaying his brutality in one incident, Hyde tortured the Avengers butler; Edwin Jarvis after helping the Masters of Evil to capture the Avengers Mansion.

Jouney Into Mystery #100