Dr. Chen Lu was his country's foremost researcher in nuclear radiation and its effect on humans. When the select members of the Chinese military sought out ways to create a costumed champion with enough power to defeat Thor, they turned to Chen Lu. They sought revenge for Thor's success in stopping an invasion of India, but Chen hoped that he could use the opportunity to give himself power enough to take over the world. Chen turned his experiments upon himself, creating the powerful Radioactive Man. He immediately traveled to New York City and challenged Thor. Chen wasted no time proving to Thor that Mjolnir (Thor's hammer) or his elemental forces had no effect against him. With but a thought he could deflect Thor's hammer like it was a gnat. He convinced Thor that any "sudden physical violence" would cause him to "blow up like an H-Bomb". With no immediate solution at hand, Thor fell victim to Chen's Hypnotic-Trance becoming his slave. Chen ordered Thor to throw his hammer away so that he could possess it, but failed to order him how far. Thor tossed it out of Chens line of sight to the bottom of the Hudson River causing him to chase after it. Chen had no way of knowing that Thor could not be separated from his hammer for more than sixty seconds without changing back to Don Blake. Unable to find Mjolnir, and believing Thor had escaped, Chen took off looking for him. Chen was hunted down by Thor once more on the roof of a building while he was about to blow up New York City. He was trapped inside a private tornado created by Thor and transported to China. Thor allowed The Radioactive Man to impact the ground upon arrival causing an atomic explosion. Chen, mistakenly, was believed to have perished from the explosion.

Chen Lu was contacted by Baron Heinrich Zemo to help form the original Masters of Evil as a counterpart for the Avengers' Thor. However, Zemo's plan to defeat the Avengers and hold New York in thrall failed because the Avengers switched up opponents and the Radioactive Man was beaten by Iron Man (Tony Stark). Another version of the Masters of Evil, this time led by Ultron, again failed to defeat the Avengers.

Retreating to Vietnam, the Radioactive Man joined the Crimson Dynamo and the Titanium Man in the Titanic Three, champions of eastern Communism and self-styled heroes of the area. The Avengers visited the country on an adventure with Mantis and the original Swordsman, but a common criminal known as the Slasher thought they were after him. He tricked the Titanic Three into battling the Avengers, but in his escape, the Slasher spilled his stolen goods, and the Titanic Three abandoned him. At some point, the threesome went their separate ways once the Crimson Dynamo left to fight Iron Man.

Returning to New York but laying low, Chen Lu was recruited by Egghead to re-form the Masters of Evil. The Masters successfully liberated Hank Pym (then Yellowjacket) from his criminal trial, convincing the public he had become a criminal. It was all part of Egghead's plan to disgrace and humiliate Pym, but Pym turned the tables of the Masters of Evil, defeating them all in time for his rescue by the Avengers.

Deported to China, the Radioactive Man worked as an agent of the Mandarin briefly, coming into conflict with Iron Man (James Rhodes) when he intercepted a shipment of sensitive equipment meant for the Mandarin.

While remanded to custody at the Vault, the prison was shut down due to a breakout, trapping the heroes and villains alike. Iron Man convinced the Radioactive Man to help him shut down a reactor that threatened to explode by using his powers to absorb the excess radiation, after which the breakout was shortly foiled.

He later appeared as an agent of Tiberius Stone, who posed as a hostage of the Radioactive Man so that he would battle Iron Man (Tony Stark). After a desperate battle, Iron Man thwarted the villain, although he couldn’t prove Stone was behind the plan to discredit Stark International.

After a period of introspection, Chen Lu came to realize that the energy fluctuations that came with his powers was often tied to emotional imbalances. He explained this as factoring into his past decisions to work on behalf of others, when really he felt superior to petty bureaucrats and megalomaniacs and would have preferred to work towards his own interests. As such, he returned to the People’s Republic of China, offering to work as the people’s champion in penitence of past deeds, which he called “the Count,” the number of every person who died or suffered, directly or indirectly, from the use of his powers.

About this time, China was attacked by militant Atlanteans calling themselves Fathom's Five. Traveling to the United Nations, the Radioactive Man was asked to aid the Thunderbolts in defeating Fathom's Five, after which he elected to remain with the team. Unknown to his teammates, the Radioactive Man had used his powers to "infect" Fathom's Five member Llyron so that he would release low levels of radiation when he returned to stand trial in Atlantis. The Sub-Mariner discovered the treachery, confronting Chen Lu and the Thunderbolts. Chen refused to apologize for his attempt at revenge on the Altantean people, but upon considering the Count, he reabsorbed the radiation which was killing Atlantis. Instead, he secretly infected the militant mole Tamara Rahn so that she would carry a time-released "virus" back to the militant stronghold and only those responsible would be affected.

When the Thunderbolts learned Baron Zemo had formed a team to kill their member Photon, they battled Zemo's team until they were forced to agree with his belief that Photon's continued existence would threaten to destroy reality. The Radioactive Man was among those asked to continue when the two teams merged into one, and he agreed, but remained skeptical, however, about the moral leadership of Zemo and Songbird.