Alex Ferguson, who has undergone emergency brain surgery, transformed the fortunes of Manchester United and turned the club into one of sport's global brands.
The 76-year-old Scot's combination of iron-fisted discipline, superb man-management and a fierce temper helped win 13 Premier League titles and under his reign United regained European prominence with two Champions League crowns.
It is a mark of Ferguson's huge influence that United have failed to regain the Premier League title since he stood down in 2013.
In a management career spanning more than 26 years, Ferguson won a remarkable 38 major trophies.
The delapidated Old Trafford he inherited on his arrival in 1986 is now a 75,000-capacity super-stadium at the heart of a global commercial empire which Forbes estimates is worth $3.7 billion (3.1 billion euros).
On the pitch, Ferguson's intimidating reputation helped nurture a group of precociously talented young players who were to form the backbone of his teams.
David Beckham, Ryan Giggs, Paul Scholes, Nicky Butt and Gary and Phil Neville emerged from United's youth set-up within years of each other.
Any player who failed to share Ferguson's drive felt the sharpness of his tongue -- striker Mark Hughes likened his dressing-downs to a "hairdryer".
Ferguson would frequently personally check where his young players were spending the evening -- and his disdain for those attracted by the bright lights eventually led him into conflict with Beckham, who would eventually move to Real Madrid.
The end of Beckham's United career came after a bizarre incident in which Ferguson kicked a boot in the player's direction, cutting him over his eye. Beckham displayed the stitched cut to the cameras.
"The minute a Manchester United player thought he was bigger than the manager, he had to go," Ferguson wrote in his autobiography.
- 'Brought greatness back' -
Dubbed "Fergie's Fledglings", that young crop of players continued the tradition of giving youth its chance instilled by United's first great Scottish manager, Matt Busby.
Ferguson "brought greatness back to United," said former Stretford End favourite Denis Law, a key figure in the celebrated United teams of the 1960s.
The son of a Glasgow shipbuilder, Ferguson cut his managerial teeth in Scotland with East Stirling and St Mirren.
He arrived at United from Aberdeen in 1986, having broken the stranglehold of Glasgow clubs Celtic and Rangers on Scottish football.
He had guided Aberdeen to an unlikely victory over mighty Real Madrid in the final of the European Cup Winners' Cup in Gothenburg in 1983.
When he took the reins, United were a moribund club who had not won the league for 19 years and were in the shadow of arch-rivals Liverpool.
Ferguson did not find success in his early years at Old Trafford and some pundits believe that in today's cut-throat management world, he would not have been given the time to find his feet.
His future at United was reportedly at stake when United travelled to Nottingham Forest for an FA Cup third-round tie in January 1990, but they won by a solitary goal.
Four months later United beat Crystal Palace in a FA Cup final replay to give Ferguson his first trophy at Old Trafford.
He would never look back.
United ended a 26-year wait for the league title by triumphing in the inaugural season of the Premier League in 1992-93, before claiming their first ever league and FA Cup double the following year.
A side of youngsters led by enigmatic Frenchman Eric Cantona claimed another double in 1996, before Ferguson's finest hour arrived in 1999, when United won an unprecedented treble of league, FA Cup and Champions League honours.
In their most famous victory, United scored twice in injury time to beat Bayern Munich 2-1 in Barcelona and win the Champions League, prompting Ferguson to exclaim: "Football, bloody hell!"
After the victory, he was honoured with a knighthood, meaning in Britain he was universally known as "Sir Alex".
Ferguson had to wait nine years for his next success in Europe's elite competition, following a penalty shootout win over Chelsea in a rainy Moscow.
Alex Ferguson took Manchester United from a moribund club into a global sporting giant
One of Old Trafford's stands is named after Alex Ferguson