Who said 'Keep your friends close and your enemies closer'?

Answer:

Some believe it was Sun-tzu Chinese general & military strategist however there is no documented history of this. Was actually first said by "Michael Corleone" in The Godfather Part II
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Actually it wasn't Sun-tzu (he said, "Know your enemy and know yourself and you will always be victorious". And while "Micheal Coreleone" did say that in the movie, it was attributed to being told to him by his father Vito. But more than that, the actual origin of the quote was from Machiavelli in "The Prince" which is the definitive primer for how to be a dictator.

This means that you always want to keep your friends close to you because they are people you can trust and rely on.
The second part of this means that your enemies are always going to be out there seeking to harm you so you want to keep an extremely close eye on them in order to make sure that they are not going to hurt you.
It means that you always have to know what your enemies are doing. Or for a reference, as a war tactic, know what the enemy is doing so you don't get ambushed.