The vast majority of comic book villains tend to stay on the path of evil, but a select number have switched allegiances to the side of right over the years.
Whether in the Marvel or DC universes, creators have been reforming and redeeming plenty of major supervillains for decades now, and though most don't manage to make the switch permanent (curse you, superhero status-quo), that doesn't make the novelty of seeing them fight alongside their old rivals any less entertaining.
Some of the most beloved and famous heroes in both the Big Two's libraries originally had villainous roots, but a lot of the time these characters' paths towards redemption were mapped out very early on or even right from the off - such was the case with Rogue, Plastic Man and Hawkeye, to name but a few.
All those characters are great, of course, but the brief time they all spent as villains has been well and truly eclipsed by their heroic personas.
That isn't the case for some of the other notable supervillain defectors though. These characters had to wait decades to switch allegiances - however brief a switch it was - but they all managed to do so in massive and oftentimes immensely gratifying ways, leaving readers desperate to see them become heroes for good.
Songbird was originally introduced as the supervillain known as Screaming Mimi (okay.... I love the name) by Mark Gruenwald, Ralph Macchio and John Byrne in 1979's Marvel Two-in-One #54, before later switching to the Songbird identity in the 1990s.
Originally an antagonist who was a member of the evil wrestling-themed supervillain team known as the Grapplers, Screaming Mimi was subjected to a process by the Power Broker that enhanced her vocal chords, thus giving her the ability to project a deafening supersonic scream not unlike the one belonging to DC's Black Canary, albeit with a few other added perks.
Following her time with the Grapplers, Mimi rejected her old wrestling title and became known as Songbird, eventually linking up with Baron Helmut Zemo and joining his faux superhero team known as the Thunderbolts.
Unfortunately for Zemo, who had planned the Thunderbolts to be nothing more than a trojan horse for the Masters of Evil to exploit, Songbird and many of the other villains recruited for the team actually grew to love playing the hero. She and her teammates betrayed Zemo, and ultimately went on to lead the Thunderbolts in its later incarnations.