#1 Ronda Rousey (12-2)
A trained judoka since her childhood, Ronda Rousey competed in the 2004 and 2008 Olympic Games in Athens and Beijing among other competitions, winning a bronze medal in judo at the latter event.
She made her amateur MMA debut in 2010, then found early success in Strikeforce the following year, before becoming the first woman to sign to UFC in November 2012.
Rousey enjoyed a two and a half year undefeated streak, where she rose to fame after a successive string of Mike Tyson-like first-round knockouts and armbar submissions.
She became the first female champion in UFC's history as well as its longest reigning Women's Bantamweight Champion, before leaving the sport after two major consecutive loses in the octagon, to Heidi Holm and Amanda Nunes.
Fortunately, Rousey had already built a rapport with WWE, having sparked a friendship with veteran wrestler "Rowdy" Roddy Piper (whom she got her nickname from) and through appearances at Summerslam in 2014 and WrestleMania 31.
Thus she inevitably followed her friend Shayna Baszler and decided to pursue a professional wrestling career in the sports entertainment juggernaut of WWE.
Though many wrestling fans were skeptical of her ability to perform before her official debut at WrestleMania 34, she has since proven herself and earned heaps of praise. She is currently RAW Women's Champion.