Redeemed Villains' or alternatively Villains turned to the Good Side is a trope found in media about villains turned heroes by their own right. Not all antagonists are villains because they are normally neutral characters, not unless they acted criminal, anthropomorphic, overhunting predator, or more bully than regular.
What made special in this case?
Many villains walk a thin line between good and evil; indeed, many villains have redeemed into remorse, sympathy or even empathy, and once arrogant villains ascend further into the path of good, often fighting against people they once protected or fought alongside, they begin to turn away from their old ways.
Originally antagonists or forces of evil, these characters turn good due to events in their lives, such as an idealism or encouragement from another hero, their positive change of heart, a good relationship with others (perhaps a successful love story), recognizing their own inner goodness and capacity for good, betrayal or any other unresolved traumatic experience in which they question whether or not the dark side is worth fighting for. However, some villains may turn for more satisfying reasons.
A Redeemed Villain, otherwise known as villain turned to the good side or Former Villain, is usually the end result of an antagonist exposed to an Outright or Purely Good hero, a Messiah, a Passively Empathetic character, a Hope Bringer, and occasionally a Charismatic Hero. In some situations, some villains turned to the good side can even become Pure Good to add drama as they are willing to be good without any despair, corruption, or negative qualities after all.