Boris Becker says Novak Djokovic has two personalities: the Zen-like competitor, and the "sweetheart who would give you his last shirt if you needed one".
Fellow Grand Slam champion Goran Ivanisevic talks of the "24-hour stress" of working with the world number one, and remembers a 13-year-old Djokovic offering him chocolate to boost his energy after their first ever practice set.
And Nikola Pilic, who coached the Serb in his teenage years, recalls a very high sport IQ and "incredible coachability".
As Djokovic prepares for next week's French Open, which could lead to a 19th Grand Slam title, BBC Radio 5 Live has spoken to three of the men who have helped him along the way.