Sir Alex Ferguson was renowned for his famous 'hairdryer treatment'.
The former Manchester United manager retired in 2013 after winning 13 Premier League titles and two Champions League trophies.
Even in his final season at Old Trafford, Ferguson was "very angry" at his players despite strolling to another league title.
"We could have gone 18 points clear but still we were in a very good position. He was very hard on us, very angry," Robin Van Persie told UEFA.
"He made everyone aware that everybody had to give their all. The training was very hard that week. He was almost punishing us. But that showed me he was a really good manager."
Retired centre-back Rio Ferdinand spent 10 incredible years playing under Fergie at Man United.
In an interview with RamboFYI, the BT Sport pundit revealed the angriest he ever saw the legendary Scottish manager.
"He [Ferguson] just turned a different colour," said Ferdinand. "He weren't happy with a lot of stuff sometimes.
"We were 4-0 or 4-1 up against Bolton and I've never seen him go that mad.
"We were 4-1 up at half-time and he went crazy because we didn't score enough goals."
No wonder Ferguson was a serial winner.
The former Aberdeen boss successfully knocked Liverpool "off their f***ing perch" and transformed Man United into one of the biggest clubs in the world.
He's arguably the greatest football manager of all-time.
Since he retired in 2013, the Red Devils have failed to win a Premier League title and currently languish in seventh.
In Ferguson's 21 Premier League seasons, Man United never finished lower than third.
Under three different managers, United have only managed a top three finish on one occasion since Fergie retired.
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