Ivo Karlović (; born 28 February 1979) is a Croatian former professional tennis player. His height of 211 cm (6 ft 11 in) makes him the joint tallest ranked tennis player in history, along with Reilly Opelka. He won eight ATP Tour singles titles between 2007 and 2016. He is a serve-and-volleyer and officially held the record for the fastest serve recorded in professional tennis, measured at 251 km/h (156 mph), before being surpassed unofficially by Samuel Groth in 2012, and officially by John Isner in 2016. In his prime, he was considered one of the best servers on tour, and held the all-time record for career aces with 13,728 (not including Davis Cup) before the record was broken by Isner on July 1 2022. This makes him one of only five players in history to surpass 10,000 aces. His height enabled him to serve with high speed and unique trajectory. Junior career Karlović played his first junior match in April 1995 at the age of 16 at a grade 3 tournament in Croatia. He played only eight tournament throughout his junior career (four singles and four doubles). In singles, he defeated a 15-year-old Marat Safin at the 1995 Junior Davis Cup. In doubles, he was known for partnering future world No. 3 Ivan Ljubičić on numerous occasions. Karlović ended his junior career with no ranking in both singles or doubles. He had an overall win–loss record of 2–5 in singles and 5–3 in doubles. Professional career 1998–2004: Beginning Although not turning pro until 2000 at the age of 21, Karlović played his first ITF futures event in June 1998 and made two finals in August 1998 and September 1999, losing both. He played his first Challenger event in December 1999. Karlović debuted for the Croatian Davis Cup team in 2000 against Ireland, where he won the dead rubber. Karlović appeared in a starting line-up for the first time in 2002 against Argentina in Buenos Aires, but he lost to Juan Ignacio Chela in the second rubber and to Gastón Gaudio in the fifth and decisive rubber. He has posted a 4–2 career record (2–2 in singles) in three ties since 2000. Karlović caused a major upset at Wimbledon when he beat defending champion Lleyton Hewitt in his first match in a Grand Slam tournament. As of 2015, Karlović remains the only player in Open tennis history, and only the