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Born on February 28, 1979, Ivo Karlović is a Croatian professional tennis player known for his exceptional serve, earning him the nickname "Dr. Ivo." Towering at 6 feet 11 inches (2.11 meters), Karlović holds the record for the fastest serve in professional tennis, clocked at an astounding 251 kilometers per hour (156 miles per hour) during the Davis Cup in 2011.