Leila O'Toole was indoctrinated into a religious cult while on an archeological dig in Egypt. She observed a sacred ceremony that offered a human sacrifice to their god but couldn't bear to be a part of the brutality, so she ran out on them. However, the cult hunted her down to the Australian outback where she met Alex Summers, the X-Man known as Havok. Mercenaries were deployed to capture Leila, but Havok mistakenly assumed they were after him. He had no choice but to expose himself and use his powers, but Leila fainted every time he shot a plasma burst near her. Havok eventually drove the mercenaries away, but not before Leila saved him from a messy end. The hunters would return to capture them, but once again Havok saved them. Leila and Havok spent a lot of time together and began to develop deep feelings for each other, and she was devastated when she thought the cultists killed Havok with a grenade.
Without her protector Leila was at the mercy of the Cult of the Living Pharaoh, but Havok soon tracked her back to their lair and traded himself for her. He was prepared to fight in their arena in a death match against armored cult members. Havok bested all but one who appeared to absorb his power, shed the armor and was revealed to be Plasma, Queen of the Cult of the Living Pharaoh. Havok expended too much energy and could not face her so he fled, but returned with Wolverine. Plasma easily defeated the feral mutant, and the more Havok used his power on her, the stronger she became. Havok pleaded with Plasma to release Leila and was stunned to see Plasma and Leila were one in the same. Leila initially lied to Havok upon their "coincidental" meeting in Australia by leaving out the part where the Living Pharaoh was her uncle and she was the rightful heir to his throne. She also neglected to tell him she was a mutant able to absorb the cosmic energies he releases. Having betrayed the man who truly loved her, Plasma fought Havok when he refused to supply her with more power. Enraged by his stubbornness, Plasma recklessly unleashed a massive energy blast through the roof of the cult's base, causing a cave in and burying herself under rock and stone.
She returned sometime later with cultists claiming to serve the Egyptian god of vengeance - the Knights of the Moon – and attacked a charity event at Grand Central Terminal in New York City. Taking several hostages, Plasma inevitably spilled innocent blood which brought her face-to-face with Ghost Rider, but she appeared to incinerate him with her incredible powers. The whole display was merely a ploy to get herself noticed by other Middle-Eastern cults so she could unite them under her rule, but Moon Knight was not going to allow that to happen. Ghost Rider returned to assist the true avatar of Khonshu as Plasma tried to escape aboard a lone train car, and although Moon Knight could not defeat Plasma in physical combat, she met her demise when the train car she was riding in collided with a wall at the end of the tracks and exploded, seemingly killing her.