They don't kick a single ball, make a single save or really do much of anything on match day. But a good manager stamps his imprint on the game nonetheless.
Who is the best? Sir Alex Ferguson has to be on the list, but is he number one? And what exactly are the criteria for being called the "best manager"?
What did you win? That's obviously the most important criteria. Managers are paid to win games. If their team does that, then they've been a success. Trophies are important, although some carry much more weight than others. And something can be said for having an impact on a club. Have they created a legacy?
From No. 15 to No. 1, here are the top managers of the new millennium.