Jannik Sinner (born 16 August 2001) is an Italian professional tennis player. He is currently ranked as the world No. 1 in men's singles by the Association of Tennis Professionals (ATP), the first Italian to reach the top ranking. Sinner has won 19 singles titles on the ATP Tour, including three majors, as well as four Masters 1000 titles and the 2024 ATP Finals. He also led Italy to the 2023 and 2024 Davis Cup crowns.

Despite limited success as a junior, Sinner began playing in professional men's events aged 16, and became one of the few players to win multiple ATP Challenger Tour titles at age 17. In 2019, he broke into the top 100, winning the Next Generation ATP Finals and the ATP Newcomer of the Year award. In 2021, he became the youngest ATP 500 champion at the Washington Open, and the first player born in the 2000s to enter the top 10 in rankings. Sinner won his first Masters 1000 title at the 2023 Canadian Open and finished the season by reaching the final of the ATP Finals and leading Italy to the Davis Cup crown.

At the 2024 Australian Open, Sinner defeated world No. 1 Novak Djokovic and then Daniil Medvedev in a five-set final, coming back from two sets down to win his first major title. He followed by winning three Masters 1000 events, the US Open, and the ATP Finals to finish the year as the dominant world No. 1.