There's an old saying that should serve as a cautionary tale to some heroes and villains in the Marvel universe that states "power tends to corrupt and absolute power corrupts absolutely." It has since been reframed and shortened over the years but continues to serve as a necessary warning.
With so many different power sources in the Marvel universe that range from alternate dimensions to cosmic forces, there have been a number of characters who have experienced the old saying quite literally after gaining incredible and sometimes god-like abilities. These are a few of the Marvel characters who gained absolute power only to be corrupted absolutely themselves.
10 The Cosmic Phoenix Force Has Turned A Few Hosts Into The Dark Phoenix
The cosmic entity known as the Phoenix Force has possessed quite a few different hosts over the years, though the most well-known is undoubtedly Jean Grey. She bonded with the Phoenix during a sacrificial attempt to save the X-Men during a space mission, and after manipulations by Jason Wyngarde/Mastermind and the Hellfire Club, her psyche shattered.
She was consumed by the cosmic power and became the Dark Phoenix after consuming a star that caused the deaths of an entire civilization. Jean sacrificed herself to stop the Dark Phoenix from reappearing, though the cosmic entity returned a few times. During Avengers vs. X-Men, it also took over Cyclops, who succumbed to its corruption and murdered his mentor, Professor Xavier.
9 King Thor Conquered Earth After Gaining Control Of The Odinforce
Following the death of Odin, Thor accepted the throne of Asgard and was empowered by the Odinforce, though he had previously been separated from his mortal half, Jake Olsen. Without this human connection, Thor became corrupted by his power. He merged Asgard with Earth and began to extend his rule over humanity.
He conquered Earth in order to keep it safe, though his methods and reasoning became flawed, and the Avengers tried but failed to stop him. Thor ruled over the planet for centuries until he realized he had chosen the wrong path, though he was able to travel back in time and stop his corruption.
8 Blackout And Darkling Have Both Been Corrupted By Their Darkforce Abilities
The Darkforce Dimension is a powerful and mysterious realm that a number of mutants and characters have a unique connection to, though it's not always a positive experience. While most characters like The Shroud or Darkstar gain incredible abilities, there have been a few who have been driven mad or even taken over by the darkness within.
Marcus Daniels/Blackout was exposed to the Darkforce Dimension and gained the ability to teleport through it but lost his mind in the process. Henrique Gallante's connection to the Darkforce allowed it to take him over to become Darkling in a bid to spread darkness across Earth before he gained control and became the second Asylum.
7 Magneto's Dark Energy Tainted Professor Xavier And Created Onslaught
Professor X and Magneto had a long history as friends before they became enemies with opposed ideals, though things changed after the Fatal Attractions event. Magneto had mutilated Wolverine, which caused Professor Xavier to reach into Magneto's mind to turn it off.
Something from Magneto's psyche reached back and rooted inside Professor Xavier. Months passed as it grew and began to manipulate Xavier, eventually transforming into the psionic entity known as Onslaught that has continued to threaten Earth and beyond after separating from Xavier.
6 The Power Of Cyttorak Turned Colossus Into A Ruthless And Uncaring Juggernaut
The Crimson Gem of Cyttorak was a mystical ruby that was found by Cain Marko. He was empowered by the ancient god as his avatar on Earth and became known as the unstoppable Juggernaut. Marko never really succumbed to Cyttorak's control, though he was corrupted by the God of Fear's enchanted hammers during the Fear Itself event.
To stop him, the X-Men's Colossus made a deal with Cyttorak to become his new avatar, and he then gained the powers of Juggernaut. However, Cyttorak began to exert more influence on Colossus, making him crave destruction and corrupting him over time. He was eventually freed from Cyttorak's curse after he was possessed by the Phoenix during Avengers vs. X-Men.
5 Mister Negative's Corruptive Touch Inverted Cloak And Dagger's Powers
Martin Li was a Chinese gang member who was taken by a rival criminal and used in an experiment to create a new drug. While most subjects died, he gained a connection to the Darkforce and Lightforce Dimensions as Mister Negative alongside other test subjects who would eventually become Cloak & Dagger.
Mister Negative had a corruptive touch that he used to convert followers to become his Inner Demons gang. When he used his powers on Cloak and Dagger, they fell under his control and became supervillains, though their powers also inverted. Cloak was able to access Lightforce while Dagger became tainted by Darkforce. Spider-Man eventually helped free them.
4 Doctor Strange Was Taken Over By Dark Magic During World War Hulk
Stephen Strange earned the title of Sorcerer Supreme after he switched from his career as a surgeon to become a Master of the Mystic Arts. Doctor Strange was part of Marvel's Illuminati, the group responsible for banishing Hulk to the planet of Sakaar. When Hulk returned for revenge during World War Hulk, Doctor Strange had his hands crushed, reducing his spellcasting ability.
He was forced to resort to dark magic by drinking the demonic soul of Zom from another dimension. He gained incredible power and abilities. Though, he soon became overcome with Zom's rage and endangered civilians until he was defeated by the Hulk. His use of dark magic caused him to lose the title of Sorcerer Supreme, and he spent years redeeming and purifying himself to take it back.
3 The Spirit of Vengeance And Galactus Turned Frank Castle Into Cosmic Ghost Rider
Marvel's Spirit of Vengeance has possessed quite a few people throughout history into Ghost Riders, dating back to the Avengers of 1,000,000 BC and modern characters like Johnny Blaze, Danny Ketch, and Robbie Reyes, who were all fighting corruption. An alternate reality version of Frank Castle/Punisher was also possessed by the Spirit of Vengeance.
However, he was left on a dead planet with no one to punish after Thanos decimated it. When Galactus arrived, he bargained with the World Devourer and gained the Power Cosmic as well, becoming the dark Cosmic Ghost Rider. He hunted Thanos across time and into different realities where he would eventually join with the Dark Guardians and launch a new quest of punishment.
2 Scarlet Witch's Chaos Magic Has Frequently Been Corrupted By Chthon
Wanda Maximoff/Scarlet Witch was raised as a child near Wundagore Mountain, which influenced the development of her powers due to the magical energies of the Elder God known as Chthon, who had been trapped within the mountain.
Chthon's chaos magic allowed him to frequently exert his control over Scarlet Witch, whose own reality-altering abilities were already becoming corruptive due to their uncontrollable nature. She attacked the West Coast Avengers under Chthon's control and later disassembled the team after her abilities caused a mental breakdown.
1 The Power Of A Million Exploding Suns Corrupted The Sentry Into The Void
Robert Reynolds was a meth addict who broke into a government facility that was creating a powerful new version of the super-soldier serum. When he drank it, he was empowered as The Sentry, with the power of a million exploding suns. Unfortunately, it also created a dark side to The Sentry known as The Void that Reynolds thought was a separate being for years.
When The Sentry lost control of his fractured mental state, The Void would take over and threaten his fellow heroes during events like Siege. However, after Reynolds was able to merge both sides of his personality, he was further corrupted and became a universal threat during Annihilation: Scourge.