And those shorts carry both of his names, Creed and Johnson. Neither Mary Anne nor Rocky are asking Adonis to cast aside his birth mother or his own history to become his father, they're honoring the person he himself has become.
Very shortly after meeting Rocky, Adonis starts calling him "Unc'." Rocky doesn't object.
Adonis' reaction to learning that Rocky has been diagnosed with cancer. The very fact that he is so concerned for his mentor's health is moving in and of itself. Furthermore, when he finally confronts Rocky about it in a reasonable manner, Adonis makes it clear that he will not participate in his upcoming bout unless his trainer accepts the necessary medical treatment:
Adonis Johnson: If I fight, you fight.
For all of his faults, Ricky Conlan truly loves his kids and is willing to put his thoughts of his legacy aside in order to secure a future for them when he has to serve his prison sentence.
Double for his trainer, who is the one who comes up with the idea for the fight, and delivers a scathing retort when Ricky initially doesn't want to do it. He clearly cares about his fighters and doing right by them.
Adonis taking care of Rocky and training for the big fight.
Rocky doesn't let his chemotherapy slow Donnie down either, forcing the kid to train even when they are at the hospital, much to the amusement of his nurses.
Adonis could really be credited for saving Rocky's life. Had Adonis not found Rocky, Rocky would have had no motivation to fight his cancer. Adonis was the one who stuck by him through it all, without him, Rocky would have slowly accepted his fate and passed away.
The above moment hits all the more when, if you recall, that in Rocky III, Rocky got his fire back training with Apollo; and in the same vein in Rocky V, when Mickey (in a flashback) admits that Rocky saved his life, too.
During the big fight, when Adonis is nearly knocked out; he briefly sees flashes from different moments of his life - the last image? The one that brings him right to his feet? The memory of Apollo, in his prime, grinning in the middle of a fight with Rocky. As if his old man personally told him to get off his ass and see this thing through.
Rocky's last Rousing Speech to Adonis before the final round:
Rocky: Look at me. I never got a chance to thank Apollo for helping me out after Mickey died. But it's nothing compared to what you've done. You taught me how to fight again. And I'm gonna go home and I'm gonna fight this thing. But if I fight, I want you to fight, too. I want you to go across this ring and knock that son of a bitch down. Can you do it? Say it.
Adonis: I'm gonna knock that son of a bitch down.
Rocky: I know you are. You know why? Because you're a Creed, and I love you, kid.
Conlan personally congratulates and thanks Adonis after the fight, and the amount of respect he has for his final opponent is obvious.
Conlan: You go and get it, chum. You the future of this division. You wear that name with pride.
After the last fight, Adonis is asked what he would say to his father if he were here tonight. The look on Donnie's face makes it clear that he never thought of that question until now, and the first thing he says is that he would tell his father that he loves him, he knows he didn't leave him on purpose, and that he's proud to be a Creed.
At the very end of the movie, Rocky and Donny walk up those steps one last time. You know the ones.
Small moment, but it seems that Mighty Mick's Gym is now looking in the best shape it's ever been, and is painted in Rocky's trademark colors of black and gold. There's even a Rocky poster and banner in the gym, meaning that nobody's ever forgotten Rocky.
