Naomi Osaka is a Japanese professional tennis player. She has been ranked world No. 1 in singles by the Women's Tennis Association (WTA) and is the first Asian player to hold the top ranking in singles. Osaka is a four-time Grand Slam singles champion, with two Australian Open and two US Open titles. Her seven titles on the WTA Tour also include two at the Premier Mandatory level. At the 2018 US Open and the 2019 Australian Open, Osaka won her first two major titles in back-to-back tournaments. She was the first woman to win successive major singles titles since Serena Williams in 2015.