Best defender in the world. Not because he is the best individually (VVD is superior IMO, and he's on par with some others), not because of his leadership, or his tackles, or his physicality, or his blocks (and they are all superb). He's the best because every single small choice he makes, is always ALWAYS optimal. And a great defender is great because of the small choices (positioning, when to tackle, how to tackle, when to run, when to be aggressive, when to foul, slowing the attack with physical presence...).
Really, watch our highlights, and every time we are being attacked stop the video, analyze where every player is, and think which movement or decision is the best for our defense, and you'll see Dias always makes the best choice. It's like he can see the future and has seen all the probable scenarios. And that's what makes him the best defender in the world.