Apollo Creed (Carl Weathers) was an electrifying character in the Rocky franchise, and from the very beginning, was the best fighter. Rocky (Sylvester Stallone) went toe to toe with brute forces like Clubber Lang and Ivan Drago, each with their particular aggressiveness and boxing style. Lang (portrayed by Mr. T) was an antagonizing boxer who talked just as fast as he threw punches, and Drago (Dolph Lungren) was a borderline machine in and out of the ring. The series proved that Creed was the best fighter of the franchise by positively contrasting him to the other boxers and by exploiting his boxing skill and knowledge through his training of Rocky.
The original film introduces Apollo and Rocky at very different moments in each of their careers. Apollo was a veteran champion who knew everything there is to know about boxing, while Rocky was an amateur searching for a break. During their first match, the respect that would bind them together over the following four films is born. Apollo barely lost against Rocky in Rocky II, and without their fight from the original Rocky, the match would have never happened anyway, giving Rocky a slight advantage. Before Apollo’s death, he had won matches against Rocky 2 out of 3 times (including their secret match at the end of Rocky III), and simply without Apollo, there would be no Rocky. He jump-started Rocky’s career, made him a fan favorite, and eventually made him the fighter that the audience loves.
After their two professional bouts, Apollo training Rocky prior to his death proves that he was the best fighter. At first, Apollo is an undefeated and arrogant champion, but after his bouts with Rocky, his demeanor changed. He put his attitude aside and forged a champion from the knowledge he had gained throughout his career. This feat separates Apollo (record: 48-1) from the other fighters who also possessed similar records (both sustaining only one loss). Clubber Lang and Drago would never be able to put their ego aside and train another competitor.
Clubber Lang was a mad dog who did not have the proper attitude to teach anyone (Apollo, while also cocky, was a superb trainer), and Drago was a soldier who operated on nothing but sheer muscle mass. The two are incomparable to Apollo because he approached boxing with respect, while the others approached it with lunacy. Apollo was one of Rocky’s best counterparts because although he was the obvious choice to win in their first fight in the original Rocky, the winning moment for Balboa was that the match lasted all 15 rounds and against an undefeated (at the time) champ. The films have always put Apollo on a pedestal from the very beginning, revealing Rocky’s unbroken spirit through his efforts to stay on his feet against one of the best to ever step in the ring.
Rocky agreed to be trained by Apollo because he knew Apollo was the only person who could treat him just as well (perhaps better) than Mickey did. Apollo helped Rocky regain that “Eye of the Tiger '' that he claimed Rocky had when he beat Apollo, and only the most well-rounded fighter can pull another out from the pits. A lot of the later films begin to play off of the friendship/mentorship of Apollo and Rocky, and that dynamic flows into the Creed series very similarly (this time Rocky as the trainer). All the fighters that are introduced in the Rocky series have a fatal flaw (even Rocky), but when it comes to Apollo the movies have always portrayed the champ as a few steps ahead of everyone else.