The player with the most aces in tennis history is Ivo Karlovic from Croatia, who has hit a total of 13,619 aces as of September 2021. Karlovic is known for his big serve and has held the record for most aces in a single season, hitting 1,477 aces in 2017. He surpassed the previous record holder, Goran Ivanisevic, another Croatian player who hit a total of 10,131 aces in his career. Other players with a significant number of aces include John Isner, Roger Federer, and Pete Sampras. However, Karlovic remains the all-time leader in aces in men's tennis.