#3 Zinedine Zidane - Real Madrid
Cristiano Ronaldo enjoyed the most successful period of his career trophy-wise under Real Madrid legend Zinedine Zidane. In their two-and-a-half-year association, they won nine trophies, including three back-to-back Champions League triumphs.
While they both left the club at the same time, Ronaldo has continued to add to his goal tally and trophy collection with Juventus. Zidane took a nine-month break to return to the Santiago Bernabeu in 2019 and deliver their first La Liga title in three years next season.
Zidane knew the value that the Portuguese star brought with him and conceded in an interview post-Ronaldo's move to Juventus that it was impossible to replace the player. He said:
"It is impossible to replace Cristiano, it does not matter who you sign. He has left the club and you can sign quality players but they will not achieve what he did at this club, but that is football."
Under him, he scored 112 goals and picked up 29 assists in 114 competitive fixtures for Madrid.
#2 Jose Mourinho - Real Madrid
Given their Portuguese connection, it was expected that Cristiano Ronaldo would have the best chemistry with Jose Mourinho. But as we all know, that was not the case.
Mourinho and Ronaldo had quite a few bust-ups during their three-year association at Real Madrid.
Though Mourinho's stay at the Santiago Bernabeu was not an especially trophy-laden one, with a La Liga title, Copa Del Rey and Supercopa de Espana to show for his efforts, Ronaldo enjoyed the most prolific phase of his career under the Special One.
Although they may not have gotten along on the pitch, Mourinho only had kind words for his compatriot and called managing Ronaldo the highlight of his highly successful career. He said:
"Coaching [Ronaldo] was the highlight of my career. He's the most professional player I've ever met.
"A coach and player may have their differences at a given time, but it ends there. I don't have any problem. I had only one problem with him, very simple, very basic."
#1 Sir Alex Ferguson - Manchester United
Ronaldo often credits Sir Alex Ferguson for setting him on the path to becoming one of the greatest players of all time. The duo developed a father-son-like relationship during their time together at Manchester United and remain close to the present day.
It was Ferguson who insisted on Ronaldo taking the iconic No.7 jersey at the club and with that delivered a statement on how much trust and expectations he had from the Portuguese winger.
It is said people who get to know icons before they reach the top are the ones who have the biggest impact on them. Rightly so, the Scot has had a huge influence on the five-time Ballon d'Or winner.
It was under Ferguson that Ronaldo first earned individual honors in the PFA Player of the Year Award, European Golden Shoe, the erstwhile FIFA World Player of the year award and obviously his first Ballon d'Or.
Ferguson will remain by some margin the greatest manager Ronaldo has ever worked with. In his 2013 autobiography, Ferguson wrote:
"Cristiano Ronaldo was the most gifted player I managed. He surpassed all the other great ones I coached at United. And I had many.
"We helped Ronaldo to be the player he was and he helped us recapture the excitement and self-expression of Manchester United teams."