On Wednesday morning the news that all Manchester United fans feared was confirmed as their long-time manager announced he would be retiring at the end of the season.
After 26 successful years, Ferguson delivered 28 trophies and 13 league titles and Souness - who played under him during his brief spell as Scotland manager from 1985 to 1986 - says he has left the club in perfect condition.
"What a legacy. He is handing over a club that from the outside looking in seems to have every single part of the club run properly," Souness told Sky Sports.
"He is Mr Manchester United - there was Bobby Charlton before him but I would say that he has even surpassed him as Mr MU because he has been so associated with the success and grown the club into one of the giants of the modern game.
"I worked under him when he took over from Jock Stein and I was the captain of Scotland. He had not moved down to England yet but he was asking me and other lads who had moved what it was like.
"I think he was always destined to go to England. As I understand it Ferguson had the Tottenham job but he turned it down because he wanted the Manchester United job."
Souness also came up against him as a manger when he was in charge at Liverpool, Southampton, Blackburn Rovers and Newcastle.
And he remembers a warning from Liverpool's Chief Executive when he first moved to Anfield.
"When I first got the Liverpool job, Peter Robinson was the CEO and regarded as the best around.
"He said to me that that their big fear is that if 'that lot' down the East Lancs road ever get their act together - that is exactly what they did under Ferguson.
"If it was not going his way then it was horrible coming up against him. To be fair to him I was at Southampton when we beat them - Roy Keane got sent off early and I think we beat them 5-2.
"He came up and had a beer and it was choking him to have this beer. He blamed the grey shirts that day. He was drinking the beer, but was not tasting it."
Souness says that one of Ferguson's greatest strengths is that he changed with the game and gave the club a winning mentality.
"From when he first went to Manchester United to today, the game has changed dramatically but he has evolved and changed. He was an aggressive old badger when he started off, a tough old cookie.
"When he was at Aberdeen he created this 'us against the world' and to a certain extent I think he did the same thing at Manchester United, but he has mellowed and he understood how the game has changed and how he managed in the early days he cannot manage today."