The Portugal captain finalized a shock move to United from Juventus on Tuesday for an initial fee of £12.9million (€15m), signing a two-year contract with the option of a third.
Ferguson was involved in luring the 36-year-old back to Old Trafford and Ronaldo has now opened up on just how big a part the legendary manager played in his decision.
"As everybody knows, since I signed for Manchester [United] at 18, Sir Alex Ferguson was the key," he told United's official website.
"I remember when we played against Manchester when I was at Sporting Lisbon. For me, Sir Alex Ferguson is like a father in football for me.
"He helped me a lot, he taught me many things, and in my opinion of course he had a big role because the relationship that we had, we keep in touch all the time.
"He's an unbelievable person. I really like him a lot and he was the main key for me to be in the position that I am, that I signed for Manchester United."
Ronaldo scored 118 goals in 292 appearances for the Red Devils under Ferguson, during which time he won the first of his five Ballon d'Or trophies.
That individual success translated to team glory, with United winning eight major honours across Ronaldo's six years at the club.
Ronaldo has since gone on to score a further 450 goals in 438 games for Real Madrid and another 101 times in 134 outings for Juventus in all competitions.
Asked why he felt the time was right to leave Juve to start a new journey, Ronaldo said: "I think it's the best decision that I have made. It's right on point in my opinion.
"I moved from Juve now to Manchester, it's a new chapter. I'm so happy and glad.
"I want to carry on again, to make history, to try to help Manchester achieve great results, to win trophies and number one of them, to win great things."
Plenty has changed in the time Ronaldo has been away from United, not least the fact that former team-mate Ole Gunnar Solskjaer is now in the Old Trafford dugout.
Ronaldo, who finished as top scorer in Serie A last season with 29 goals, is hoping to pick up from where he left off by helping Solskjaer get off the mark with a first trophy as United boss.
"We had a chat, but of course I'm going to have time to speak with him face to face, to know what he expects," Ronaldo said.
"As you know, I played with him for two or three years at Manchester United so I have a good relationship with him but now with a different role, I'm a player and he's a coach.
"But it doesn't matter, my relationship with him is great and as I say before, I'm there in Manchester to help the team achieve his results and the coach can count on me for whatever he wants. So I'm available for everything."
Ronaldo is in line to make his second debut for United when they take on Newcastle United at Old Trafford on September 11.
"I have a fantastic history with this amazing club. I was here at 18 years old and of course I'm so happy to be back home after 12 years," he said. "I'm really glad and looking forward to my first game.
"With all the stadiums full of supporters, it's not the same that we had one year ago, those empty stadiums. The fans, they are the key, and I'm so glad.
"The Manchester United fans, they are special, I know, I remember very well. I know they still sing my music which has made me feel even more happy.
"My commitment is to give everything on the pitch, like I did before, like I do it all the time, and try to do my best, help the team score goals, make assists, win games, and I hope to see them very, very soon."