#9 Gail Kim
Gail Kim is widely considered to be one of the best female wrestlers of the past two decades. However, one could also rightly argue that she hasn't received due credit during her two stints with the WWE. Kim is a former WWE Women's Champion, and belonged to an era when the likes of Trish Stratus and Lita dominated the women's division.
Gail harboured hopes of taking the women's division in the company to greater heights, and was signed back after she left the then TNA. However, Gail has since revealed that she was always held back, and wasn't happy with WWE's direction (or lack of) for the women's division, and for her character.
In an act that summed up her WWE tenure, Gail eliminated herself from a battle royal in what would be her final WWE match, and refused to work for the company ever again. She has since won the TNA Knockouts Championship on seven different occasions, and was inducted into the TNA Hall Of Fame in 2016. WWE definitely missed the boat with one of the greatest women's wrestlers of this generation, who could've spearheaded the women's revolution in the company.