Emma Swan

Morrison described her character at the beginning of the first season as "broken, damaged and worldly." During the fourth season finale, "Operation Mongoose," Emma absorbs the power of the Dark One into herself to save Regina. In order to successfully create a dark version of Emma, Morrison explained that "In order to build Dark Emma, I've been doing a bunch of research there with some of their mythology books and old fairy tale books and just looking back through the history of swans and the etymology of 'Swan'" and explained that Emma's rate of evolution "challenged [her] on a daily basis." Emma became the primary antagonist of the fifth season's first half, until the end of the season's eighth episode when it is revealed that she was never actually evil and was an anti-villain during that time.
Morrison's portrayal of Emma has received praise, with some reviewers noting a feminist twist in the depiction of fairy tales and a strong female lead. She is loosely based on the title character of the fairy tale "The Ugly Duckling," a swan which was lost and raised by ducks, before finding its birth family and recognizing its true nature, while her Dark One persona is loosely based on Odile from the ballet ''Swan Lake''. It is revealed in the season 6 episode "Tougher Than the Rest" that she chose the last name Swan when she was young after a friend mentioned that story. Provided by Wikipedia