Commodus similar to Caligula
Commodus seems based on the infamous Roman emperor Caligula. They were both corrupt and at odds with the senators. However, the biggest similarly was their incestuous relationships with their sisters. Both emperors killed at the hands of their own Roman country men.
One might want to check out the infamous 1979 movie CALIGULA in order to find other similarities (if one wants to wade through all the repulsive pornographic scenes within its 2 and 1/2 hour running time!).