Sir Alex Ferguson said that he was "absolutely devastated" at the loss of Walter Smith. Graeme Souness described his former Rangers assistant as a "colossus". Pep Guardiola also paid tribute to the "humble, intelligent and genuine man"
A huge outpouring has been made by the football world for Smith's passing at the age of 73.
Ferguson described his former assistant at Manchester United and Scotland as "a special person".
Smith was the Dundee United's coach at the time. He was also part of Ferguson’s backroom team at 1986 World Cup. Smith became Ferguson's number two at Old Trafford 2004. The pair was seen together at a Loch Lomond golf day in September.
Ferguson, 79, said that Ferguson was a "great friend" for many years. "In all those years you dealt with a man who lived his life with great moral compass and offered friendship to so many people.
"His contribution was tremendous to football. He will be greatly missed."
"He took the time to help so many people."
Smith's first association with Rangers began after the World Cup. He was initially Souness' assistant, before becoming manager in 1991.
The next decade was one of dominance, including the 1993 domestic treble. This helped Ibrox match Celtic's 1997 record of nine consecutive titles. Smith received an OBE in the same year for his services to football.
Souness, in a joint statement with Sir David Murray, former Rangers chairman, said that "Scottish football had lost one of it's finest" and added that "even in the proud History of Glasgow Rangers Walter Smith stands out like a colossus".
They said: "Walter had an enormous effect on our lives, both as a leader and as a mentor and wise and trusted advisor. But he was also a dear friend and close friend. He was a generous man who made time to help so many people.
Smith was instrumental in reviving the Rangers career for Ally McCoist, who had been denied first-team opportunities during Souness' reign.
McCoist was awarded the European gold boot in consecutive seasons. He later became assistant to Smith with Scotland, Rangers and Rangers.
Talksport spoke out about Smith's "like my second dad". He added: "He was the greatest husband, father, friend, and everything you could want in a man." "I can't even tell you how distraught I am."
McCoist had been keeping Richard Gough, a former Everton and Rangers defender, appraised of Smith’s declining health in recent months and it was he that broke the news to Smith.
Radio Scotland's Gough said, "It's very tragic news, but we knew it was coming." "He had been home for the past 10 days to be with his loved ones."
The football world will always remember the towering figures
Pep Guardiola from Manchester City was perhaps the most surprising tribute. He met Smith through his work with the League Managers Association in England as a technical consultant.
Guardiola stated that he was aware of Walter's remarkable management career prior to joining the Premier League. "But I've had the chance over the past five-years to see how humble, intelligent and very genuine he was.
Walter was a great friend and I always enjoyed our time together. We had planned to meet up again for dinner. I am very grateful to have been able to meet him. I also send my condolences and sympathies to Walter's family who have lost an exceptional man.
Gordon Strachan, Smith's successor as Scotland manager, told Radio Scotland that the news "took me by surprise for a while".
He said, "The game I love and the reason why I'm still involved in it is people - and Walter was one of the greatest factors in my love of this game." "When I met Walter, my life was better."
David Moyes, West Ham's manager, took over Everton's job. He said that he was a "great Scottish manager, but an even greater man"
He said, "He was honorable, he displayed great dignity, and always showed such class," he concluded. He was a mentor and friend, and I felt privileged to have known him."