Katie Taylor (born 2 July 1986) is an Irish professional boxer and former footballer. She is a two-weight world champion and the current undisputed lightweight champion, having held the WBA title since 2017; the IBF title since 2018; and the WBC, WBO, and Ring magazine titles since 2019, as well as having held the WBO junior-welterweight title in 2019. Following her victory over Delfine Persoon in 2019, she became one of only seven boxers in history, female or male, to hold all four major world titles in boxing—WBA, WBC, IBF and WBO—simultaneously, along with Bernard Hopkins (2004–2005), Jermain Taylor (2005), Cecilia Brækhus (2014–), Terence Crawford (2017), Oleksandr Usyk (2018–2019), and Claressa Shields (2019–).

In her successful amateur boxing career, Taylor won five consecutive gold medals at the Women's World Championships, gold six times at the European Championships, and gold five times at the European Union Championships. Hugely popular in Ireland, she is credited with raising the profile of women's boxing at home and abroad. Regarded as the outstanding Irish athlete of her generation, she was the flag bearer for Ireland at the 2012 London Olympics opening ceremony before going on to win an Olympic gold medal in the lightweight division. Taylor turned professional in 2016 under Matchroom Boxing, and is known for her fast-paced, aggressive boxing style, which has been compared to that of a male boxer. As of July 2019, Taylor is ranked as the world's best active female lightweight, and number one pound-for-pound boxer by BoxRec.