William Rolfson, the son of Apocalypse and Famine in the Age of Apocalypse, grew up to be the evil mutant known as Nemesis. He was sent by his father to kill the X-Men and successfully killed a small group of young mutants and the Scarlet Witch. Enraged by the death of his daughter, Magneto hunted down Nemesis and destroyed his physical body, leaving his spiritual essence, which was then sent back to Apocalypse and put into the near indestructible armor that was made by the Dark Beast. And thus, Holocaust was born.
Holocaust was created by Scott Lobdell and Roger Cruz and first appeared in X-Men: Alpha #1 which was part of the Age of Apocalypse storyline. Two years earlier, his 616 counterpart was featured in a preview in X-Men: Stryfe's Strike File #1.
Major Story Arcs
Age of Apocalypse
When Nemesis, who was then called Holocaust, was given his next assignment, he was to keep a watch on an Infinites (the army of Apocalypse) manufacturing factory. There, Holocaust was assaulted by Sabretooth, Wild Child, Blink, and Rogue. Holocaust was first attacked by the eager Sabretooth, but, after a few minutes of vigorous battle, seemingly dispatched of the mutant. Blink, enraged by her friends alleged death, attacked Holocaust. It was then that Holocaust proved the durability of his new armor by emerging from a tub of acid unscathed after being pushed in by Blink. Because Blink was obviously being defeated, Rogue interfered the battle and may have defeated Holocaust had he not teleported to the safety of his father Apocalypse's domain. Though he had hoped to teleported to safety, he arrived in time to interfere in a battle between Apocalypse and Nate Grey, the X-Man. Though Nate seemed to have easily dispatched Holocaust with a powerful psionic blast, he soon recovered to interfere the fight again. When Holocaust attacked Nate, Magneto took the initiative to attack Apocalypse. The battle between Holocaust and Nate was fairly even, until Nate found a small shard of the M'Kraan Crystal and stabbed it into Holocaust. The Crystal combined with Holocaust's unique genetic make-up seemingly transported the two combatants into the earth-616 dimension, which is true Marvel Universe continuity.
The Onslaught Saga
While it is unknown where Nate Grey was transported after the Crystal event, Holocaust wound up in space near Magneto's space station Avalon. The station, unknowing of Holocaust's origin, brought the frozen mutant into their protection. Holocaust awoke in time to kill his guard, the mutant known as Rusty, and absorb his life force, which put him back to his normal power. Holocaust then fought the leader of the space station, Exodus. The fight ultimately resulted in the destruction of the space station. When Holocaust returned to earth, he found the psionic being Onslaught and embraced the being as a chance to get back at Nate Grey. Holocaust became an agent of Onslaught willingly. Holocaust's first assignment under Onslaught was, to Holocaust's satisfaction, to attack Nate Grey. Holocaust was barely defeated, and was forced to retreat. Onslaught later revealed to Holocaust that he had sent him merely to test the mettle of the X-Man.
Son of Apocalypse
In one event occurring from Nate Grey's time manipulation, Holocaust became trapped in time. He was then forced to join the superhero team the Exiles in order to return to the correct time line. Holocaust replaced Blackwing who had been near-fatally wounded in a previous mission. In the foreign time line, Holocaust leaned that Apocalypse had died. This left Holocaust's father's empire without a ruler. This fact was so tempting to Holocaust that he forgot about his time issue and went forth to claim the throne. He would have done so, too, had he not stumbled upon the even more tempting power of the M'Kraan Crystal once again. Holocaust remained with the Exiles, believing that their resourcefulness in time traveling would aid him in acquiring the Crystal. The Exiles' ventures eventually lead them to the Panoptichron before it became their base, and found an evil alternate reality form of Hyperion ruling as an emperor there and controlling the M'Kraan Crystal. Holocaust, enraged at Hyperion's possession of what he believed was rightfully his by blood, attacked the emperor, but to no success. Hyperion broke Holocaust's armor and absorbed his essence, killing him.
Powers and Abilities
Holocaust's primary mutant power was the ability to absorb various forms of ambient energy, including the life energy of other beings, into himself. He could use this drained energy to augment his other mutant attributes and was fully sustained by these energies, therefore requiring no food, water, air, or even sleep to sustain his physical and mental health. By purposely channeling the energy he'd absorbed, Holocaust could grant himself superhuman strength sufficient enough to lift up to 2 tons. As a result of using his absorbed energy to enhance his strength, his musculature was far more efficient than that of an ordinary human. His muscles produced less fatigue toxins during physical activity than that of normal humans and he could potentially exert himself almost indefinitely, provided he could continue to absorb energy as needed.
Outside of his armor, Holocaust's body is in an almost intangible state. As a result, he is virtually impervious to all forms of physical injury. However, he must continuously absorb the life energies of others in order to maintain his form outside of his armor.
Holocaust could generate concentrated beams of plasma, which he often used in combat situations. At his peak, he could generate plasma blasts reaching a temperature of about 1,000,000 degrees Farenheit. He could also propel himself through the air, under his own power, at great speeds. He did so by creating super heated air currents that propelled him. While at his peak, he was able to reach speeds up to MACH-1, approximately 760 miles per hour.
Onslaught was able to alter Holocaust's brain engrams in order to render him resistant to most forms of telepathic assault. His engrams were altered to such a degree that he was rendered undetectable telepathically.
As Nemesis, Holocaust was also able to redirect energy into a negation effect on others' powers. Since losing his physical form, he no longer seems to possess this ability.
Once Warren Worthington arises as a new potential Apocalypse host, Famine brings her son, William Rolfson, out of hiding and offers his services to Worthington. Naming himself Genocide, this version of Rolfson fought X-Force and incinerated Wolverine's body defeating him and almost killed him. Later Genocide destroyed an entire town and its thousands of inhabitants following Archangel's orders.
Eventually, he sought out the Celestial Gardener, offering himself as the true heir to Apocalypse, and was deemed worthy of the Death Seed. However before he could attain his new role as Apocalypse's successor, the Apocalypse Twins arrived and murdered the Celestial and almost all of Clan Akkaba, Genocide included.
In Other Media
In the X men episode "one man's worth" the world is changed and and holocaust has a brief blink and you missed it cameo fighting alongside the x men!
In the video-game "x men legends 2" holocaust is a boss you fight while trying to defeat the stepford cuckoos
Holocaust had two figures, one was a small figure that included a spear and missile, while the other was a build a figure from a Marvel Legends wave. Both are under the name Nemesis