The Portuguese trickster was the target of intense abuse following his role in the sending off of Rooney in the World Cup quarter final victory over England.
Ronaldo said at the time that he would leave Manchester United, with Barcelona and Real Madrid waiting to pounce, but he has since revealed the special relationship with Ferguson.
"Sir Alex is a very caring coach and I have a relationship with him that goes far beyond what is usual between a player and the coach," Ronaldo told the Daily Mirror.
"In fact, I can even say I signed for United because of him and it is down to him that I am still with United in England.
"At the end of last season (2005/06) he was one of the most influential people in my decision."
Ronaldo insists he now regrets declaring he would leave United and he is adamant that the best is yet to come.
"There are moments in life when we all react on impulse when it would be wiser to stop, take a breath and think in a more rational way," Ronaldo added.
"That's what I should have done after all that controversy concerning Rooney and me. I acted in haste when I said there were no circumstances under which I would stay.
"Everybody makes mistakes. But the story had a happy ending.
"I assure you the best is yet to come. And the best will be more titles, which are the icing on the cake."