Answer
Novak Djokovic was coached by Boris Becker for three years from 2014 to 2017. Becker was a successful player himself, winning six Grand Slam titles. He was also a successful coach, helping Djokovic win three Grand Slam titles during their time together. Becker and Djokovic parted ways in 2017 after Djokovic lost in the quarterfinals of Wimbledon.