Former United and Real Madrid star Beckham was asked what makes Ferguson the greatest.
He told manutd.com: "Everything. It's everything about him, and everything that he does is always for the good of the club. He doesn't do things just to please himself, he does them because he thinks that's what is best for the team, the club and the fans. That's why he's loved the way he is and why he has the respect that he's got.
"Of course, part of that is down to the success he's had and the trophies he's won over the years, but the majority of it is down to the way he does things. He commands that respect and every player that comes to Manchester United is the right player for the club.
"He doesn't just bring players in because they're some of the best in the world, he does it because they fit into the Manchester United family. I feel so honoured to have played under him for so many years and I'll never forget the moments I shared with the greatest manager in football."