Naomi Osaka (大坂 なおみ Ōsaka Naomi) is a Japanese professional tennis player. She is the reigning US Open champion in women's singles. Osaka has a career-high Women's Tennis Association (WTA) ranking of No. 6 in the world, which she achieved in October 2018. She has won two titles and reached four finals on the WTA Tour.

Osaka first came to prominence at the age of sixteen when she defeated former US Open champion Samantha Stosur at the 2014 Bank of the West Classic, which was her first time in the main draw of a WTA tournament. She reached her first WTA final two years later at the 2016 Toray Pan Pacific Open, which took her into the top 50 in the world rankings. Her breakthrough year was 2018; in March she won Indian Wells, beating former world number ones Maria Sharapova and Karolína Plíšková in the first round and quarterfinals respectively, before defeating current No. 1 Simona Halep in the semifinals. In September, she won the 2018 US Open, defeating 23-time Grand Slam champion Serena Williams in the final, and becoming the first Japanese player to win a Grand Slam singles tournament.

Osaka has an aggressive playing style, with a powerful serve that can reach 125 miles per hour (200 km/h).

Naomi Osaka was born in Chūō-ku, Osaka to a Haitian father, Leonard "San" François, and a Japanese mother, Tamaki Osaka.

Naomi and her older sister Mari were given their mother's maiden name for practical reasons when the family lived in Japan. Her father was born in Haiti and went to New York University before moving to Japan, where he met her mother and later married her.

In racially homogeneous Japan, Osaka is considered hāfu, which is Japanese for biracial. Her Japanese grandfather was furious when he found out that her mother was romantically involved with a black man. As a result of the interracial relationship, her mother did not have contact with her family for over ten years. In a 2016 interview, Osaka said: "When I go to Japan, people are confused. From my name, they don’t expect to see a black girl."

Osaka and her sister Mari, who is also a professional tennis player, have played together in doubles. Osaka moved at the age of three with her family to the United States where she currently resides in Florida. She graduated from Elmont Alden Terrace Primary and Broward Virtual High School.

After her win against Serena Williams, Osaka's grandfather stated that he wept watching his granddaughter on television. "It still hasn't sunk in for me yet. The moment she won, my wife and I rejoiced together. I was so happy, I cried," he told public broadcaster NHK. "I hope she stays healthy and continues her good work. I also hope she wins at the Tokyo Olympics [in 2020]," he said.

Osaka has been described as Japanese, American, Japanese-American, American-Japanese, Haitian-Japanese, and Haitian-American-Japanese. Being raised in the United States while having a mother who is Japanese and a father who is Haitian-American contributes to Osaka's multi-ethnic identity. Osaka has dual Japanese and American citizenship but she is not fully fluent in Japanese.

Osaka practiced at Utsubo Tennis Center in Japan. USTA Billie Jean King National Tennis Center in Long Island. and Pembroke Pines' public court in Florida. Her tennis club was the Harold Solomon Institute (Florida Tennis SBT Academy), ProWorld Tennis Academy. In 2007, she won the "National Public Parks Girls' 14 Doubles Championships" with her sister Mari.

Osaka made her debut at the 2011 ITF Women's Circuit in a first round qualifying match in Montego Bay on 17 October 2011, the day after her fourteenth birthday.

Osaka's father made the decision to register her with the Japan Tennis Association when she began her career. She turned pro in September 2013, and made her WTA Tour main-draw debut at the 2014 Bank of the West Classic, after defeating Alla Kudryavtseva and Petra Martić in qualifying. She was then pitted against 2011 US Open champion Samantha Stosur and came from a set down to defeat the Australian in a match lasting 2 1/2 hours.

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