4. Mesut Ozil
Ronaldo has played with some of the greatest playmakers of this generation - Toni Kroos, Luka Modric, Xabi Alonso, Paul Scholes, etc. However, there was no one with which he had better on-field chemistry than Mesut Ozil.
The German international spent only 3 seasons with Real Madrid. However, 109 appearances were enough for him and Ronaldo to form one of the best striker-midfielder partnerships of this era. Ozil at Madrid was a superior player than the Ozil we see nowadays at Arsenal - the playmaker was much more agile, more aware of the final pass, and he could create chances out of thin air. Having the best finisher in the world ahead of him helped Ozil rack up some stunning assist numbers during his time at the Spanish capital - he had over 70 assists in just three seasons.
When the midfielder left for Arsenal, a lot of people were disappointed. Ronaldo was one of those people, as he and Ozil shared a telepathic connection that he has had with only a few players across his career.