Katherine Cadwallader Douglass (born November 17, 2001) is an American competitive swimmer. A versatile swimmer who competes in many events, Douglass won her first major international medal at the 2020 Olympic Games and won three medals at the 2022 World Championships. Douglass then won six medals, including two golds, at the 2023 World Championships. At the 2024 World Championships, she won five medals, including two golds. Douglass won four medals, including two golds, at the 2024 Olympic Games; she became the Olympic champion in the 200 m breaststroke.
Douglass competed for the University of Virginia during her NCAA career, which lasted from 2019 to 2023. She is considered one of the greatest swimmers in NCAA history. In her three NCAA Division I Championship meets in 2021, 2022, and 2023, she helped Virginia win the team competition. At the 2021 NCAA Championships, she won one gold medal and six silver medals. At the 2022 NCAA Championships, she won seven gold medals. At the 2023 NCAA Championships, she won seven gold medals. Douglass won the Honda Sports Award as the best college female swimmer in 2022 and 2023.