Pietro Maximoff has sped across the fine line between good and evil countless times since he first appeared in 1964. Created by Stan Lee and Jack Kirby, he was intended to be an antagonist for Marvel's heroes, softened only by his protective nature towards his twin sister Wanda (a.k.a., the Scarlet Witch).

His villainous roots are hardly surprising considering the Maximoff twins believed Magneto to be their father for decades, joining his Brotherhood of Evil Mutants out of obligation. Nevertheless, heroism has long been in their hearts, and Quicksilver has never been afraid to jump into action to help keep the universe safe. Here are 5 of his most heroic feats, and 5 of his most villainous.

10 Heroic: He Joined Cap's Kooky Quartet

Quicksilver spent a long time battling alongside the Brotherhood of Evil Mutants but when Magneto was defeated and removed from Earth by the cosmic being Stranger, Pietro and Wanda fled. The pair were taken in by the Avengers.

With Earth's mightiest heroes in need of some well-earned rest, Captain America took the twins and a rogue Hawkeye under his wing, creating the second generation of Avengers – lovingly known as Cap's Kooky Quartet. While Quicksilver's rebellious nature was impossible to tame, the team defeated the likes of Doctor Doom and Kang the Conqueror with ease, proving Quicksilver's true worth as a hero.

9 Villainous: He Disapproved of Wanda's Marriage

Quicksilver's relationship with his sister has always been ... questionable. They have stood by each other through world-altering events, but Quicksilver can be very overprotective of Wanda, and slightly prejudiced too.

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After a stint living with the Inhumans, Quicksilver returned to Earth with his new lover, Crystal, to see his fellow Avengers. He and Crystal are welcomed with open arms, particularly by Wanda. But when she tries to share her own good news that she and Vision plan to be married, Quicksilver completely loses his cool, shouting: "I am the HEAD of our family and I FORBID you to love that thing!" before storming off, disowning her.

8 Heroic: He Led the Knights of Wundagore

A group of scientifically-evolved animals gifted with human intelligence by experimental researcher, Herbert Wyndham, banded together to create the Knights of Wundagore in the 20th Century to protect Wundagore Mountain from otherworldly threats.

When their base was seized by the Acolytes, Wyndham (now calling himself the High Evolutionary) appointed Quicksilver the leader of the Knights. Pietro led the humanoid creatures to victory throughout the Seige of Wundagore, helping them reclaim their former home. He would later rejoin the team as an intelligence-gathering scout, proving himself to be an advocate for outcasts and underdogs, willing to fight against injustice.

7 Villainous: He Turned to Crime

Steve Englehart firmly believed Quicksilver worked best as a villain, consequently leading the character down some of his darkest paths. When Quicksilver discovered Crystal was seeing another man, he flew into a vengeful rage, gradually spiraling into a crime spree.

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Aiming to become the "King of Evil Mutants" he not only led members of crime organization, Zodiac, in their misdeeds but also joined forces with Soviet Russia. With the Communists seeking revenge on Hank Pym, Quicksilver lured Wanda to their base to use them as test subjects to develop their own superhumans. Why did he choose his beloved sister? Because she married Vision, of course.

6 Heroic: He Helped Defeat the High Evolutionary

Quicksilver gladly joined the Avengers Unity Division, established by Captain America following the events of Avengers vs X-Men, in an effort to bridge the divide between mutants and humans. They soon became involved in a battle between the Low Evolutionary, one of Counter-Earth's last humans, and Herbert Wyndham himself.

Discovering that he and Wanda had been kidnapped and experimented on by Wyndham as children, Quicksilver joined the Low Evolutionary's fight against the High Evolutionary and delivered the final blow which sent Wyndham fleeing from Earth, stopping his barbaric experiments once and for all.

5 Villainous: He Betrayed the Avengers ... A Lot

Despite being their teammate on occasion, Quicksilver has been quick to betray the Avengers too. Not only did he capture the West Coast team with plans to kill them in West Coast Avengers #33 - #36, but his rage-filled battle against Earth following his break-up with Crystal led him to attempt to frame the Avengers for treason.

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When his plan to have the heroes locked away failed, he brought the West and East Coast Avengers together and planned to kill them all with nuclear weapons! Many of his villainous deeds from this era were eventually explained away with brainwashing, but it's unlikely Englehart developed these stories with Quicksilver's redemption in mind.

4 Heroic: He Fought in Godly Battles ... And Won

Quicksilver is clearly respected by his peers, having been invited to fight amongst Marvel's mightiest kings. He joined Hercules and Amadeus Cho when they stormed Olympus Group headquarters, battling side-by-side with Zeus himself to ward off Amazonian warriors. He even saved Wolverine during this battle, killing the Huntsman when he saw his ally was wounded and in danger.

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Quicksilver was later summoned to battle against the Thunderbolts when they launched an assault on Asgard. Battling against Mister X, who was armed with the Spear of Odin, Quicksilver used his speed to defeat the villain and help the Norse realm survive the onslaught.

3 Villainous: He Stole Terrigen Crystals

Finding himself powerless after the events of M-Day, Quicksilver decided to experiment with the Terrigen Crystals in an attempt to restore his abilities - against Black Bolt's wishes. Murdering Goran to steal the Crystals, then kidnapping his daughter, Luna, to expose her to them - giving her powers far too early - Quicksilver fled to Earth.

U.S. Government agents came after him, aiming to steal the power-enhancing property. They were nearly successful, too. The Crystals would have fallen into the wrong hands had Black Bolt not arrived, his whisper ultimately causing mass destruction and opening conflict between the Inhumans and U.S. Government.

2 Heroic: He Saved Earth From the Grandmaster and Challenger

When Earth found itself in the midst of a giant game between the Grandmaster and Challenger, many of its heroes became caught in stasis, trapped inside themselves. Quicksilver was one of the affected heroes, awakening in Avengers Auxiliary Headquarters to spot a speeding orb of light circling the other impacted heroes.

Believing it to be the source of the stasis, he convinced Wanda and Synapse to enhance his superpowers so he could catch the lightning-fast ball of light. He was able to catch the orb, disappearing into a grey dimension. His heroic sacrifice released the trapped heroes, allowing them to work together to defeat Challenger and save Earth.

1 Villainous: He (Technically) Caused 'House of M'

Scarlet Witch uttering No More Mutants during House of M in Marvel Comics

One of the worst events to befall Marvel's mutants, 'House of M' may never have happened without Quicksilver's meddling.

When Scarlet Witch began losing control of her growing power, killing a number of Avengers, it quickly became evident she was beyond help. In an attempt to save his sister, he convinced her to warp reality to create their own perfect haven. With his encouragement, Wanda went ahead with the plan, but this world eventually crumbled as memories returned to the heroes inhabiting it. When Magneto discovered Quicksilver was behind the plot, he killed the boy, pushing Wanda over the edge, creating an entirely new reality without mutants.

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