Klaus Voorhees was a convicted criminal who was assigned to become the lab assistant of renown medical researcher and humanitarian Professor Shecktor. At the side of the scientist, Voorhees learned a great deal about serpents and chemistry, but soon grew envious of the Schecktor's achievements and the respect he received from his peers. Eventually his jealousy evolved into hatred, and Voorhees decided to murder Shecktor by making a cobra from the lab to bite him. Voorhees would then cause himself to be bitten by the cobra (making the whole incident look like an accident), but he would then consume an experimental antidote for the snake venom. Putting his plan in motion, Voorhees succeeded in murdering Shecktor. Unknown to Voorhees, however, the serpent he chose had been irradiated as part of an experimental process for the immunization of humans against snake venom. The antidote saved Voorhees' life, but the irradiated poison of the cobra endowed him with powers similar to those of a snake. Deciding to use his new abilities for criminal enterprise, Voorhees adopted the costumed identity of the Cobra. His first attempt at crime involved the concoction of a cobra-serum in order to transform the world's populace into similarly snake-powered slaves. His plan, however, was thwarted by the thunder god Thor, who would become the Cobra's arch-nemesis in the early years of his villainous career.
After numerous attempts at crime, the Cobra teamed up with Mister Hyde to gain revenge on Thor, and despite their defeat, they began a long partnership together. Their next team-up was on behalf of Loki. On his urging, the two kidnapped Blake’s nurse and love interest, Jane Foster but were again defeated by Thor. The pair crossed the paths of many heroes, most notably Daredevil and Spider-Man.
The Cobra parted company with Hyde for a time, joining with the original Viper’s Serpent Squad and battling against Captain America and the Falcon. Later, he was freed from prison by a new Serpent Squad led by the female Viper. He immediately challenged the Viper’s leadership, but she quickly and soundly defeated him. The Squad’s objective was to raise the sunken continent Lemuria to aid Viper’s ally, the warlord Krang. The Viper, however, was operating under the influence of the Serpent Crown, and the Cobra suddenly felt out of his element-- after all, he was only in it for the money, and not the resultant clash with the authorities and Captain America (in his identity of Nomad.) The Cobra and Viper were the only two to escape the authorities, but the police managed to track them back to the U.S. In the final battle, the Cobra tried to cut and run, but Viper, enraged by his cowardice, shot him in the back. Nevertheless, Nomad and the Cobra seemed to be the only ones to escape the hideout as it went down in flames.
The Cobra and Mister Hyde, working on behalf of the Purple Man, suffered yet another defeat from Daredevil, were remanded to Ryker’s Island prison. The Cobra used his powers to escape, but willingly left Hyde behind when they ran into difficulties. Enraged, Hyde swore vengeance on his former partner. Mister Hyde would later return to stalk the Cobra, who was at this time was seriously fearing for his life. Hyde was stopped by Spider-Man, after a long and ferocious battle, by getting stunned after being knocked out a high window.
The Cobra was recruited by the Sidewinder to become a member of his new organization, the Serpent Society. The Cobra remained with this organization for a long time, rising to become one of Sidewinder's most trusted lieutenants. When Viper returned to take over the Society, the Cobra (among with Society members Anaconda and Cottonmouth) decided to support her as the new leader. He began to question Viper, however, when she revealed her plan to mutate everyone in Washington DC into serpent-like creatures. Eventually, the Cobra rebelled and single-handedly defeated Viper, who he later turned over to Captain America. With Viper's takeover thwarted, the Serpent Society was reorganized. Bitter over his betrayal by various Society members, Sidewinder resigned from his position as team leader, leaving the Cobra in his stead.
This began a new period of Voorhees’ life, as his recent successes lent him a determination to re-invent himself for his new position of leadership, The Cobra sought out the one person that he still feared above all-- Mister Hyde. After going one-on-one with his former partner, the Cobra succeeded in besting him. Flushed with new confidence, he renamed himself King Cobra, and the long grudge match between the two seemed to be over.
Under King Cobra’s leadership, the Society first tried to put Diamondback on trial for betraying them by developing a relationship with Captain America. The trial was a disaster. Not only did Diamondback escape (with the help of Sidewinder), but he lost the support of her friends within the group, and Diamondback led Captain America and Paladin to the team to take them down. With its members scattered, the Serpent Society remained too fragmented to be considered a significant threat as it was under Sidewinder’s direction. Indeed, it was only after creating new “Sidewinders” with similar teleportaion technology as their namesakes that the team could once again operate at full capacity.
King Cobra appeared as one of the many villains who were freed upon a massive breakout of the Raft staged by Electro. Although many were thwarted by the new Avengers, King Cobra managed to get away but became the first such escapee who the new hero Toxin hoped to bring to justice. Toxin used Mister Hyde as an informant on his former partner, successuflly tracking him down, and King Cobra was brought back to prison.
When the Commission on Superhuman Activities persuaded the Thunderbolts to track down super-villains and recruit them to join the pro-registration side of the Civil War|Superhuman Registration Act, King Cobra decided to join the Thunderbolts.