Are there four kings or three kings in tennis today? Or two-person turn? Who can give me a reason?

It is the four great kings, but the three kings are more accurate and will turn into a two-person turn. Murray makes it hard to see when he can reach the heights of Federer, Nadal and Djokovic. Of course, except the three of them, Murray is much taller than others. Federer, Nadal and Djokovic are absolute kings, but Federer is old and his state is not as good as before. Nadal is still at his peak, but Djokovic has surpassed him. Djokovic has reached the peak and is almost invincible in the world. Men's tennis may become a duet between Djokovic and Nadal, and Federer may fly with them for a while, but the possibility is not great, and Nadal is more likely. There is also the possibility that Murray will rise and Djokovic will dominate the world, but Djokovic and Nadal are most likely to turn.