As The Avengers are known as the greatest collection of heroes in Marvel Comics, but occasionally a former villain can switch sides and the squad.
From Avengers mainstays such as Venom, even the most dastardly villains can have a change of heart. Though many former villains have ed the team, only a few left an impression on readers to be counted among the best the Avengers have to offer.
Echo/Ronin
For some villains, turning good is a simple proposition, but for characters such as Daredevil, she eventually realized that the Man Without Fear was actually her boyfriend, Matt Murdoch.
Distraught over all of the trouble she caused, Echo fled the U.S. and tried to make things right. After befriending Wolverine, she began a new career as Ronin and assisted the New Avengers on a mission in Japan. She hung around as a member for a while before eventually drifting away from the group and shedding the Ronin persona.
Sandman
Even though Sandman is most ed as one of Spider-Man's best villains, he has switched sides on several occasions. Always straddling the line between good and evil, Sandman was never actually a full-fledged member of the Avengers, but he nearly earned that distinction.
After assisting the Avengers, Sandman was surprisingly asked to be a probationary member, and fought valliantly when the main team was kidnapped by the Tetrarchs of Entropy. Unfortunately for Sandy, the life of an Avenger was too much for him, and through a series of miscommunications he departed the group and eventually returned to crime.
Rogue
Originally part of the Brotherhood of Evil Mutants, X-Men as a force for good. She became an established member of Xavier's mutant squad, and eventually worked herself up to a leadership role within the group.
The Avengers and the X-Men haven't always gotten along, and they even nearly went to war with one another on several occasions. To quell tensions, the Avengers Unity Division was created, which was a place within the organization for mutants. Naturally, Rogue ed the group and was an active member on and off until the group was disbanded.
Venom
The powerful symbiote known as Venom has gone through several different iterations in Marvel Comics. The Agent Venom era saw the symbiote transformed into a suit of armor that granted the wearer extraordinary powers.
Agent Venom ed several teams, but it was his stint with the Secret Avengers that was perhaps his biggest run. Flash Thompson's work as Agent Venom impressed Black Widow.
Red Hulk
General "Thunderbolt" Ross has been a constant thorn in the side of Red Hulk, he kicked his antagonism into overdrive and went on a rampage to destroy Bruce Banner.
Once his energy draining powers were removed, Red Hulk became a force for good and was quickly recruited into the Avengers fold thanks to Captain America. While his teammates were wary of him, Red Hulk proved to be an important asset to the team and has continued to be a powerful antihero in the Marvel Universe.
The Winter Soldier
Captain America's sidekick Bucky Barnes made his Winter Soldier, a dangerous Soviet assassin who opposed his old partner in Captain America.
With the help of Black Widow, Bucky shed his assassin programing and became a hero. He was even Captain America for a brief time before he became a fixture within the Avengers organization. While he no longer was a villain, his methods often clashed with some of his more squeaky-clean Avengers teammates.
Quicksilver
Long thought to be a mutant, it was only recently revealed that Pietro Maximoff was actually given his powers by the High Evolutionary in the latter's quest to expedite human evolution. Quicksilver earned his name by being Marvel's resident speedster, and his debut saw him the Brotherhood of Evil Mutants in opposition to the X-Men.
Without settling his score with Xavier's team, Quicksilver and his sister Wanda, aka the Scarlet Witch, soon ed the Avengers and made up one half of its infamous second roster. Despite a seeming downgrade to the team, "Cap's Kooky Quartet" proved to be abundantly capable in battle. Pietro has remained a part of the Avengers lore ever since and even did stints with the X-Men as well.
Hawkeye
Clint Barton's time as a villain has been largely forgotten by all but the biggest Marvel Comics fans, but his skills did make him a fearsome foe. Along with Black Widow, Hawkeye spent a brief period terrorizing the likes of Iron Man before making the switch to the side of good.
Barton's change for good came when he simply expressed his desire to reform and was helped by the Avengers to change his ways. ing the Maximoff twins in the second iteration of the team, Hawkeye has been a part of some of the best Avengers rosters of all time. Even when the team branched out into the West Coast Avengers, Hawkeye was there to lead them.
Vision
The advanced android known simply as Ultron. During Ultron's fight against the Avengers, he constructed Vision to oppose his creators, and imbued him with extraordinary powers.
In an ironic twist of fate, Vision turned on his creator and sided with his former foes in an effort to defeat him. With adjustments and enhancements, Vision ed the team and has been a constant presence in the comics as well as in the MCU ever since.
Scarlet Witch
Like her brother Pietro, Wanda Maximoff was created by the High Evolutionary, even though fans were led to believe she was a mutant for most of her existence in the comics. The powerful sorceress debuted as part of Magneto's Brotherhood of Evil Mutants but very quickly turned good after fighting the X-Men.
Though she wasn't an original member of the team, Wanda's tenure as an Avenger has been one of the longest and most impactful. Her brushes with antiheroism have made her a fascinating character to follow, and her Avengers status carried over when she ed Hawkeye as a leader of the West Coast Avengers.