He said Fergie's will to win stood out but even then "you would never have expected the success he had afterwards".
"He came in (to United) '86 after Ron Atkinson had been sacked. I had him from October '86 to the summer of '88," Moran recalled today.
He pointed out "it took him a long time before he got the first trophy over the line", but he "was afforded the time then".
While the "prima donna era" of football players only came in after Moran retired, Ferguson "did have to control the players".
"There were a lot of strong characters in the dressing room at that time," he told the Today With Pat Kenny radio show, referring to the likes of Paul McGrath and Norman Whiteside.
McGrath explained how he clashed with Ferguson over his drinking, but in hindsight believes that the coach was right.
"Sir Alex had a vision for Manchester United. Rightly so he thought that the alcohol thing was not a good thing for Manchester United. I think in the end and rightly so he got rid of people in that trap."
But he said that years later Ferguson offered him an olive branch after an Aston Villa cup game, by coming up to him and saying "well done big fella".
"He's an amazing man.
"This is the big thing now. This is one departure that is going to affect the club in a huge way. For 26 years now he's been winning them trophies. It's going to be a very difficult thing for any manager to come in, whether it's Mourinho and Moyes or anyone else. Are the fans going to take to you?"
Ex-Ireland midfielder Ronnie Whelan said: "I was extremely surprised when I woke up this morning to hear the news. He didn't give any indication on Saturday after the game against Chelsea that he was going to retire.
"It is a loss to the Premiership in general and to football. He will probably go down as the greatest manager ever. He was very harsh with people but he was also very fair."
The Liverpool legend added: "He was also very good at building teams year after year, you see how the Premiership has developed. He was just a magnificent manager.
"Fergie hasn't always been a shining knight when he is away from the football pitch (referring to politics). We have seen Mourinho's record over the years. It would be Mourinho for me (to succeed Sir Alex)."
Ray Houghton, who was a teammate of Whelan's for Ireland and Liverpool, believes Ferguson will miss "his day-to-day involvement" with Man United.
He also highlighted the crucial role Bobby Charlton played in bringing Fergie to the club and ensuring he wasn't sacked during the difficult early years.
"Sir Bobby has been there throughout Sir Alex's tenure for 26 and a half years so he's relied on Sir Bobby's knowledge of Manchester United. He's gone to him in an advisory role as well," Houghton said.
He said there would be a queue of applicants for the vacancy.
"A lot of managers now will be looking to take over that job. It's going to be a very tough one to take on after all Sir Alex has done for United," he added.
Man United fans in Ireland were today mourning the loss of a great manager.
Celebrity lawyer Gerald Kean, a devoted supporter of the club who has meet Ferguson on several occasions, said: "He was very intelligent as a manager, very sharp, very bright, very focused, very hard-working and a disciplinarian – but you could talk to him.
"Sometimes I had my clients come to me with a problem and I would ask them 'would you talk to Alex Ferguson about it' and they would always say 'yes'. They felt they could do that. But at the same time you knew not to cross him.
"I'm totally selfish. I'm not happy at all. I would have been happy for him to stay on until he was 90. It's a happy day for football fans from other clubs.
"On the field, he has always been an extraordinary man in not only winning so many championships but building so many teams. He did that by bringing players in gradually and building teams slowly."