A chain reaction in an atomic reactor, a result of a terrorist attack, accidentally created a force that absorbed the electrolytes of the nearby humans' brains, granting the explosion of energy a rudimentary sentience. The creature went on a rampage, absorbing more intelligence and killing the "donors" until he was stopped by Hulk and Hawkeye.
Later, an accident at a research complex designed to record brain waves of people, collected and re-created the Zzzax entity, who was promptly defeated by the Hulk again. Then, Stark International made the mistake of purchasing the central power core from the same research complex, which released Zzzax once more. Dr. Bruce Banner, the alter ego of the Hulk, was nearby, and he defeated Zzzax by drawing him into a stellar-powered generator, which dissipated Zzzax into space.
Zzzax was revived through the powers of Graviton, who wanted an ally with the powers of Zzzax to fulfill his team comprised of those who could control the four fundamental forces, of which Zzzax represented electro-magnetism. Graviton hoped to defeat the Avengers, but they failed. In fact, in their first confrontation with the team, Hawkeye shot a cable arrow through Zzzax and into a puddle of water, easily dissipating the entity.
Somehow, Zzzax was imprisoned by the espionage agency S.H.I.E.L.D. after this encounter, and was stored in a large insulated tube in New Mexico. There, the army general General "Thunderbolt" Ross wanted to undergo an experiment that would imbue him with the powers of Zzzax in order to defeat the Hulk. Unfortunately, the experiment backfired, and Ross' psionic energy was absorbed into a revived Zzzax-- Ross' consciousness governed Zzzax's body while Zzzax's own personality was submerged. Ross, as Zzzax, fought the Hulk, but Ross was convinced that he inhabited a monster's body, and Zzzax fled, distraught.
During a later experiment at Stark International, Tony Stark, a.k.a. Iron Man, ran an experiment that pulled Zzzax out of the air, overloading his generator. Zzzax claimed to have gained enough power to free himself of Ross' influence, which must have returned to Ross' body. Zzzax succeeded in defeating Iron Man, but Iron Man connected Zzzax to the generator and to liquid nitrogen at the last moment, shorting out the entity.
Once again, Zzzax's remains were remanded to S.H.I.E.L.D. custody. S.H.I.E.L.D. was later interested in taking down the mutant known as Cable, and S.H.I.E.L.D.'s Agent 18 unleashed Zzzax where Cable would be forced to battle him. Ultimately, Cable was able to defeat Zzzax with an open water main, and Zzzax dissipated.
Nevertheless, Zzzax 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, Zzzax managed to escape.