#3 Tony Roche
Tony Roche has had the distinction of working with four former World #1 ranked players: Ivan Lendl, Patrick Rafter, Roger Federer and Lleyton Hewitt.
Legend has it that Lendl hired Roche just so that he can learn how to volley like him. Roche coached Swiss legend Roger Federer from 2005 to 2007. Roche had a significant influence on the grand slam record-holder.
Federer was already world #1 when he began working with Roche but the Australian mentor ensured that he remained there. It is rumored that Roche didn't have a contractual agreement with Federer and accepted payments by the week.
Roche was also a successful tennis player winning the French Open Singles in 1966. Apart from Singles, he also excelled in Doubles and Mixed Doubles winning 13 Grand Slams and two Grand Slams respectively.