Triple-Evil is an entity from the Avengers, the premier superhero team of the Marvel universe - it is an extra-dimensional incarnation of evil.


And it came to pass that there were three great beings, supreme in their realm, who guarded and shaped that realm, and were sum and substance of it. And the three were themselves, and the three were the Trion. And countless ages ago, even as such as they reckon time, the Trion took action to safeguard their realm. Three acting as one, created a sphere of perfect darkness and into that sphere they poured all their darkness, all the evil tendency within them concentrating it within, entrapping it, imprisoning it forever. Imprisoning it all...all but for one tiny jagged fragment of dark, concentrated evil...which tore through a rift in reality and into another realm (Earth 616). And there, in that realm, the pyramid-shaped shard began a great journey, a long hungry journey across the vastness of space.
And it came to pass... That the universe reacted to the presence of the evil that journeyed through it...forming opposition, even as a body forms defenses against disease. And these fragments of light, these triangles, were three in number...and they, too, did journey...tumbling through trackless space, awaiting a time they would be found...found and used against the taint that had invaded their world. ...The shard of darkness journeyed across space. Wherever its path took it, it radiated foul, corrupting, evil. And wherever its path took it, it found resistance. Might empires. Lone planets. All who encountered it fought against it-- and all were lost. their best and bravest were enticed into dreams and death...and their bodies corrupted, became soldiers in the service of the darkness. That which had been their ships became armor for the shard. And their planets, their civilizations destroyed...all the fire that once burned within their races became part of the shard's power. And its journey continued and its power grew.
Eventually, an unnamed alien champion found the first triangle of light that the universe had created as an anti-body for the Triple-Evil shard/pyramid. He battled the Triple-Evil Pyramid alone and fell before it. To defeat the pyramid, one needed all three pieces of light, and as he only had one, he was corrupted and his soul was absorbed. His triangle fell on the surface of the pyramid.
The second triangle was found by the alien Skrull, and ended up being merged with 3-D Man, who was later merged with Triathlon. The third triangle was merged with Jonathan Tremont, who formed the Triune Understanding to combat the coming threat of the Triple-Evil.
When Kang showed the Avengers several possible future threats that could lead to the destruction of humanity, one of them he showed was the Triple-Evil Pyramid.
Quasar and the Living Lightning detected the Triple-Evil pyramid headed toward our solar system at incredible speeds. They left their asteroid base and chased it.
Jonathan Tremont and several Avengers had taken off in a space ship to confront the Triple-Evil. They met up with some other Avengers as well as Quasar and Living Lightning. Together, they went to examine the pyramid up close. When Living Lightning touched it however, there was a flash of light, and suddenly, all the Avengers found themselves inside illusions of their wildest dreams. They stayed in those illusions for weeks until Captain America overcame them, and thus freed the other Avengers from the illusions as well.
When they awoke, they were inside the Triple-Evil Pyramid. They saw a few aliens controlling the machines they had been hooked into for the illusions. When the Avengers tried to leave, they discovered that the aliens, as well as the chamber in which they awoke, were only more illusions, and suddenly the illusions were dropped and the Avengers were attacked by countless soldiers of the Triple-Evil Pyramid. At first the soldiers put up almost no challenge, but then, as the fight went on, they adapted and became immune to the Avengers' powers. Tremont then released the full extent of his power granted to him by his third shard. His power, which was the antithesis of the Triple-Evil, scared off the soldiers, but Tremont lacked the power to destroy or even seize control of the pyramid. In an attempt to gain that power, he tried to take the second shard away from Triathlon, and merge it with himself. However, Triathlon found the place where the champion with the first shard fell, and Triathlon seized that shard. Now with two shards, Triathlon easily took Tremont's shard and assembled all three pieces thereby granting him great cosmic power. With his newfound power, Triathlon grew in size, and struggled against the entire pyramid in a battle of tremendous power. Eventually, Triathlon triumphed, and seized control of the pyramid.
Triathlon, who was now in complete control of the Triple-Evil Pyramid's tremendous power, as well as his own now-cosmic power, started to use the stolen energies of the pyramid to move it toward Earth to rejoin the ongoing war against Kang the Conqueror who had declared war on Earth, and had conquered it successfully in the weeks the Avengers were trapped in the illusions. Eventually, they made their way back to Earth orbit where the pyramid encountered and begin to battle Kang's orbiting headquarters, Damocles Base. The pyramid then made a huge projection of Captain America's form, many times its normal size, to battle a giant form of Kang.
The Triple-Evil pyramid, under Triathlon's control, continued to exchange fire with Damocles Base as well as continue to project Captain America's form. Damocles Base focused most of its power at the pyramid instead of at the heroes attacking it from outside and from Earth. The pyramid took extreme damage that slowed it down. However, the shield over Damocles Base was destroyed, and the Avengers quickly destroyed the base, ending the battle.
Triathlon returned to the Triple-Evil Pyramid after the conclusion of the war against Kang to dissolve it and release any of its remaining energies. He left to free all of the enslaved souls.