It also stars Hulk Hogan (or Hollywood Hogan) as the character Thunderlips.
Warning: Wikipedia contains spoilers
Rocky III begins with Rocky winning the title from Apollo Creed (played by Weathers). Creed retires, and Rocky becomes an accomplished champion, making ten defenses of his belt. Meanwhile, he buys a mansion, appears on several magazine covers and makes several TV show appearances, and becomes a household name as he appears on everything, from t-shirts to chocolate bars. While this is all happening, Clubber Lang is coming up on the ranks, beating everybody put in front of him. He becomes the number 1 challenger, while Rocky gets reconstructive nose surgery and starts to learn how to talk in public.
Rocky and Thunderlips have a charity boxing-Wrestling match, with Lang watching at ringside. There, Lang starts taunting the boxing champion, but the champ just will not listen to him, so Lang just adds to his own frustrations.
Rocky has a statue unveiled in Philadelphia, but Lang shows up there too, and tells Rocky that his fights had been fixed after the Creed rematch. Rocky, confused, asks Mickey, his trainer, to explain, and Mickey tells him that his fights after winning the championship were not fixed, but the opponents Rocky faced weren't championship caliber. He tells Rocky that Rocky was faced with underqualified opponents to protect him from another dangerous fight like his two fights with Creed. To that end, he strongly advises Rocky against fighting Lang since the challenger is not only brutal, but he also has a superior fighting spirit while Rocky has gotten too comfortable as champion.
Rocky, feeling he needs to prove to himself that he is worthy of the title of Heavyweight champion of the world he has, signs to fight Lang, the number 1 contender. Unfortunately, he fails to take his training seriously and Mickey fears disaster as a result. Lang and Rocky meet at Philadeplphia's Spectrum coliseum, and during a melee before the fight, Mickey is accidentally pushed and hits a tube, and is critically injured. Rocky and Lang fight, but Rocky's mind is on Mickey, and he loses the belt, by a knockout in the second round. When he returns to his locker room, he and Mickey have their last conversation, and Mickey passes away on Rocky's arms.
Next, Rocky is in deep self doubt, but Apollo comes in to help, and takes him and Adrian to Los Angeles, where Apollo talks to him about "recovering the eye of the tiger," his critical fighting spirit, and starts teaching Rocky how to box with rhythm. Rocky attempts to learn from Apollo, but his regrets and fears sap his resolve and Apollo is frustrated. A heart to heart with Adrian occurs in which Rocky admits his fears and she reassures him that she will be with him no matter what. Thus inspired, Rocky returns to the training with renewed vigour.
Rocky then goes for a rematch versus Lang, and with people around the world watching, he recovers his world Heavyweight championship and his self respect, with a knockout in three over Lang at the Madison Square Garden in New York. Rocky and Apollo then are shown entering a gym, where Apollo wants Rocky to do him a favor: Apollo wants a third fight with Rocky, even though this one will only be a practice bout with amateur boxing helmets on. The movie finishes with Apollo and Rocky swinging crosses at each other.
The movie contained a song by Survivor (music group), that many consider a rock classic: Eye Of The Tiger, which became a chart topper the year the movie was released, in 1981.