"The greatest bit of advice he gave me was: 'be yourself, be your own man. Don't try to follow anyone else'," Boothroyd told the Guardian.
"He will always pick up the phone or phone you back if he can't get to you the first time. I've never known him not to call back, which is a mark of the guy.
"We have a good relationship. He has been kind enough to say some nice things about me, and the respect I have for him is huge. To do what he has done over 20 years, at the biggest club in the world, is a fantastic achievement.
"I like him because he has got time for the little people, and that is how you measure a bloke. I would like to think I could be in it (the game) for as long as he has. That is how you're judged - over time and by what you win.
"When you take a team like Aberdeen to the Cup Winners' Cup Final and break the Celtic-Rangers duopoly in Scotland, it takes some doing.
"Then, when you go to Manchester United, an absolute giant who were struggling, and take them to where they are now -- he is up there with the best of all-time."