Adolfo Daniel Vallejo Álvarez (born 28 April 2004) is a Paraguayan professional tennis player who reached a career-high ATP singles ranking of World No. 60 on 31 August 2026, establishing himself as the current No. 1 player from his country. As a junior, he achieved the top ranking in 2022 and made history by winning the prestigious Orange Bowl in 2021, becoming the first Paraguayan to claim that title. After winning his maiden ATP Challenger title in São Léopoldo, Brazil, in March 2024, he continued to rise, and in 2026 he broke into the world's top 100—the first Paraguayan to do so since Ramón Delgado—and made his Masters 1000 debut in Madrid, where he defeated Grigor Dimitrov and Learner Tien. He also made his Grand Slam debut at the French Open in 2026, advancing to the second round after Cameron Norrie retired. However, his tournament ended in controversy when he made sexist remarks about chair umpire Ana Carvalho, leading to a record €65,000 fine from Roland Garros organizers.