Klopp is delighted with the progress of the Dutchman, who arrived in January from Southampton for a club record £75m.
"He's a nice boy, to be honest, that's the most important thing," said Klopp. "But we did not take him because he is nice, but because he can play football well, but that he's such a good boy, of course, it helps him to settle down in the group, and he does a good job.
"There is no doubt that he is a good player, our four other central defenders are good and that only helps, and if you have a lot of control, you need the right qualities for your defenders.
"His body language is brilliant, to be honest, he looks like a leader, a warrior and already a real Liverpool player."