Ronnie Raymond was a carefree and popular high school student, who cared more about sports and cars than fixing the world's problems. But he joined an anti-nuclear activist group, all in order to impress a far more socially conscious girl who he had a crush on. When Ronnie and the group showed up to protest an experimental nuclear power facility, the protesters became violent and sought to destroy the plant, and Ronnie attempted to stop them. At the plant was its designer, Dr. Martin Stein, whom the anti-nuclear activist group knocked Stein unconscious, they also tied up Ronnie Raymond after he attempted to stop their plans, leaving them both to die in the ensuing explosion. The explosion then breached the nuclear reactor, and caused an atomic blast. But instead of killing them, the incident fused Raymond and Stein into one immensely powerful metahuman being.
Ronnie became the one who physically controlled the new, fused body as he was the only one conscious during the accident, but Prof. Stein was also active inside of his mind, "talking" to Ronnie and guiding his actions mentally. Ronnie quickly realized the accident had given them incredible super powers. He now had flaming hair and pale white eyes, could emit so-called fusion blasts from his hands, phase through solid objects, and re-arrange atomic matter, with the exception of anything organic. They decided to use this newfound power as Firestorm, and became a prominent Super-Hero. Firestorm quickly gathered a roster of enemies, like the sociopathic Killer Frost.
At first, Martin Stein did not recall any of his time as Firestorm, with only Ronnie retaining a conscious memory of it. This would lead Stein confused as to his "missing time," but Ronnie eventually explained to him what was happening, and soon, Stein would remember their merging. Still, at first only Ronnie could initiate the Firestorm matrix to form, as he was the one who conscious during the creation. When Ronnie graduated high school, he transferred to the University of Pittsburgh, where Martin Stein taught, so they could be in close proximity to each other when Firestorm was needed. Quickly making a name for himself as a Super-Hero, Firestorm became the youngest member of the Justice League of America.
After the events of the Crisis on Infinite Earths, Firestorm would undergo a series of massive changes. Professor Stein was diagnosed with a form of terminal cancer. Believing that his death would mark the end of Firestorm, Stein wanted to do one last, important heroic act, and he thought he could use his power to force the world's biggest military countries to give up their stockpiles of nuclear arms.
This caused both the nuclear super-powers of the United States and the Soviet Union to try and stop him. As part of this retaliation, the Soviets sent their own Nuclear Man, an experimental soldier code-named Phozar, to defeat Firestorm. The battle between the two nuclear powered metahumans resulted in a massive nuclear explosion, and the creation of a new Firestorm, now made up of three different people. This Firestorm was made from the physical forms of Ronnie and Phozar whose true identity was Mikhail Arkadin. But his mind was controlled by an amnesiac Martin Stein, who didn't know who he was or how to really control the Firestorm matrix.
This new Firestorm would discover that he was actually Earth's Fire Elemental, and became a far more environmentally conscious Super-Hero. Stein would then take complete control of the Firestorm persona, and let Ronnie and Arkadin return to their former lives, now independent of the Firestorm matrix. Stein then took to the stars, leaving Earth behind. When Ronnie Raymond developed leukemia, he returned to Earth, and not only cured Ronnie of his illness, but allowed him to keep his Firestorm powers independently. After this, Ronnie joined the Justice League offshoot, Extreme Justice, and briefly, the Power Company. He later became a reserve member of the JLA.
Firestorm's luck would run out though, as during the event known as the Identity Crisis, he was impaled by villainous Shadow Thief. Realizing that he would soon die, Ronnie took to the sky, getting far away from civilians, and he exploded. But the Firestorm energy needed a new host, and it found one in down on his luck Detroit teenager Jason Rusch. It took him some time for Jason to control his powers as Firestorm, and he fused with various other people, sometimes unintentionally, like his best friend Mick Wong. When he was asked to go out to space on a crucial mission during the Infinite Crisis event, Jason encountered the Fire Elemental that was Martin Stein. Feeling he needed Stein's guidance, especially after what happened to Ronnie, he convinced the Fire Elemental to join with him as Firestorm once more.
Eventually the Martin Stein aspect of Firestorm departed once again, and Jason began to fuse with Lorraine Reilly, Ronnie Raymond's old friend and fellow nuclear hero Firehawk. Jason also began dating a young woman named Gehenna, who is a teleporter. Sometime after starting his heroic career, this version of Firestorm is evenasked by Batman to be a member of the Justice League. But this new Firestorm's life would be radically altered once again when the Blackest Night began, and Ronnie Raymond was resurrected by the Black Lantern Corps as one of their members. The Black Lantern Firestorm, who later called itself Deathstorm, forced Jason into fusing with him, and then murdered Gehenna, making Jason an unwilling participant in the killing of his own girlfriend.
Post Infinite Crisis
In the final battle of the Blackest Night against Nekron, the Entity of Death, Ronnie is restored to life properly alongside Jason, with the two separating from Firestorm. Ronnie is confused, seemingly not remembering anything that happened since his death years before. But Jason is furious with Ronnie over killing Gehenna, an act Ronnie has no memory of. Although there is at first great animosity between both halves of the Firestorm matrix, they eventually learn to live with each other, and fuse into Firestorm when the need arises.
After the events of FLASHPOINT, reality was altered once again, and all previous version of Firestorm are erased from history. Ronnie Raymond is once again a high school student and football player in this timeline. During a terrorist attack on his school, Ronnie's classmate Jason Rusch produces a vial given to him by Professor Stein, which contains the "God Particle", one of Stein's creations. This God Particle transforms both teenagers Jason and Ronnie into new versions of Firestorm.
Unlike before, Jason and Ronnie now have powers individually, and do not have to combine to become Firestorm. When they do combine however, it is as the being they called Fury, which is very aggressive and powerful, which forces Ronnie and Jason to join together only in extreme emergencies. When the two Firestorms form into Fury, Jason is the "brains," to Ronnie's "Brawn," much as Martin Stein was to Ronnie in the pre-FLASHPOINT timeline.