Holocaust was a powerful mutant native to the Age of Apocalypse time-line who has clashed with the X-Men on behalf of Apocalypse - although Holocaust claimed to be the son of Apocalypse it is all but impossible to verify and given Holocaust's death at the hands of King Hyperion the truth will likely never be revealed. For a while Holocaust was named Nemesis but by the time of his demise he was back to using the name Holocaust.
Holocaust was sent to the X-Men's base at Wundagore Mountain by Apocalypse in order to prove his worth. Known as Nemesis at the time, he claimed to be the son of Apocalypse.
Nemesis was sent to kill as many of Magneto's young students as he could while the X-Men were off fighting Apocalypse's Horsemen. He was defeated in battle by the Scarlet Witch, although he was able to kill her. He left before the X-Men returned and was embraced by Apocalypse as his newest Horseman.
During Apocalypse's blitzkrieg launched against Europe and Asia, Nemesis joined Apocalypse in Japan. They murdered thousands of humans and captured Sunfire, but before they could kill him, Sunfire unleashed a nuclear level plasma blast. Nemesis absorbed the blast, saving himself and Apocalypse.
When Apocalypse returned home to recuperate, Nemesis, now charged with Sunfire's energies, was left to take care of Japan. A small squad of X-Men attacked him. Using Sunfire's energy, Nemesis was about to murder Quicksilver. Enraged, Magneto used his powers to tear Nemesis apart from the inside out. The X-Men retreated, many of them injured, and left the burnt corpse of Nemesis for dead.
Nemesis awoke in the labs of the Dark Beast and was fitted with a transparent armor that would not only channel his energy but also contain him and keep him from dissipating. He took the name Holocaust and would eventually become a Horseman again.
In the days leading up to the fall of Apocalypse, Holocaust faced off against Sabretooth and Wild Child in Chicago. Holocaust was winning and, in his excitement, revealed the secret location of an Infinite processing plant. Wild Child took this information back to the X-Men who used it to save thousands of lives.
Defeated in Indianapolis by the X-Men, the beaten Holocaust returned to his father's side. In the final battle of the Age of Apocalypse, Holocaust fought the Sinister-created Nate Grey. Grey stabbed Holocaust with a shard of the M'Kraan Crystal, which sent both of them into the mainstream Marvel universe where Holocaust continued to wreak havoc.
Eventually Holocaust was placed onto the Exiles when they visited the Age of Apocalypse reality. Immediately attacking his team members, Holocaust decided to escape the battle to initially seek out Mister Sinister and take back his Father's Earth, but became distracted by the resonance frequency of the nearby M'Kraan Crystal. After finding the crystal in a military base, Holocaust interrogated the research staff who told him there was another object making similar energy emissions as the crystal. The technicians' equipment led Holocaust back to the Exiles and the Tallus. There, Holocaust and the Exiles worked together, using both the Tallus and the M'Kraan Crystal, to teleport to the Panoptichron where they found out that King Hyperion had taken over the operation. Furious that this one man would seek to enslave the Son of Apocalypse, Holocaust attacked Hyperion. Hyperion quickly dealt with Holocaust by cracking open his shell and "eating" the pure energy that he was made of effectively killing Holocaust.
Powers and Abilities
Holocaust's primary mutant power was an 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. As a result, he required 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 sufficient superhuman strength 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's reflexes were heightened to levels that are beyond the natural physical limits of the finest human athlete. 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 Fahrenheit. Holocaust could 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 that rendered him resistant to most forms of telepathic assault. His engrams were altered to such a degree that he was rendered undetectable telepathically. As Nemesis, he was also able to redirect that energy into a negation effect on others' powers. Since losing his physical form, he no longer seemed to possess this ability.