This is all mostly introduced in the first couple of chapters, apart from one, but if you got confused here you go.
1-2 Badge Trainer Beginner
3-5 Badge Trainer Novice
6-7 Badge Trainer Intermediate
8 Badge Trainer Advanced (Usually Last Stage Pokemon)
ACE Soldiers, Top-16 Contestants Professional (Almost Always Last Stage Pokemon)
ACE Squad Leaders, Excellent Top1 Contestants, Rookie/Weak GLs Expert
Standard Gym Leaders, ACE/Military Commanders, Frontier Brains Elite
Elite 4, Certain Frontier Brains, Certain GL Master
Champions and y'know. The GOATs. Champion / ????